Check that the power cord is connected to the computer or monitor and is plugged into a working outlet. On systems where the monitor is separate from the computer, each has it's own power cord. Both must be plugged in to a working power source.

      Most monitors use the same type of power cord as the computer. So you can switch the cord to see if on of the cords is bad or not getting power.

If the cord does have power, yet the computer does not come on, it could be a failed power supply. See:
Murf's page on power supplies.
Also see:
Local    ATX Power Supply Frequently Asked Questions from Compute-Aid. This article additionally, has good information about how computers are cooled and how to properly ventalate your system.

      Today there are two basic types of power supplies in use:
AT/ISA which is turned off and on by an internal switch activated by linkage to the front panel.
ATX which is turned on and of by commands from the motherboard. This type allows the computer to "Sleep". When testing to see if an ATX power supply is working, it is important to have the motherboard and at least one component (hard drive) connected, as these power supplies need to have a load. Since it must have a connection to the motherboard to turn it on, it can be much more difficult to test. In a computer where it was changed from an ISA to an ATX (motherboard accepted either), the extra motherboard plug (for a server MB) was plugged in along with the ATX connector

If the power supply is not getting a good connection to the cantrol switch or motherboard, it may fail to turn on. That could be fixed by restoring the connection. If the power supply thinks it's voltage output is incorrect, it will turn itself off to protect the computer components.

Any of these could cause your problem.

This usually indicates that a component is connected wrong. If this occurred right after connections were changed inside the computer box, check the connections very closely. With many components, the connector can be reversed. The power supply is designed to shut down if it senses this to prevent damage to all components on the system.

The first and easiest test is to disconnect all external devices. You only need the Monitor and Keyboard connected (and, of course, the power cords). Although rare, external connections can cause a computer to not power on

Check the Power Source. A bad power switch, circuit breaker or wiring can cause a voltage drop that can cause such symptoms.

If this just occurred, without any internal changes, it could be a power supply failure. Power supplies have very closely regulated voltages on many of it outputs. If it sense the voltage outside of the limits, it will normally shut down to protect the components. This would take a professional to verify.

New power supplies are usually $30 to $50. If you are technically skilled, they are not that difficult to replace.

However, in addition to various power ratings (200 watts and up), there are two major types of power supply's:

See Murf's page on power supplies for more information.

      Check that the cord connecting the computer to the monitor is plugged into both components. The plug is a D shape (roughly) with 15 pins. In some computers, some pins may be missing. That is normal as not all of the pins are needed. Some manufacturers make the cord to work only on that device. Check that none of the pins are bent.

      This 15 pin connector is for VGA monitors (Video Graphics Array). Older color monitors will not work with a VGA video card and have a different plug on them. CGA monitor use a 9 pin D shaped connector.

      Another check is to disconnect all external devices. You only need the Monitor and Keyboard connected (and, of course, the power cords). Although rare, external connections can cause a computer to not boot at all. In one case PC will not boot! (Virtual Dr.) malfunctioning computers were not networked.Yet, they had common symptoms. But they were connected to a common printer. When disconnected from the printer switch, the computers booted normally. It's easier to disconnect external devices than starting inside the box.

      Check the Power Source. A bad power switch, circuit breaker or wiring can cause a voltage drop that can cause such symptoms.

      If these are not the problem, check the Video card itself. If it is an older computer, sometimes removing and re-inserting a device will restore contact. If is is a new installation, did it ever work?

      This could be a compatibility problem. To isolate what the conflict might be, you should remove all devices except the Video card and memory chips. Then try the boot again.

      If it still stays the same, take out memory chips (if you have more than one set) until you have the minimum chips needed. On SIMMS 30 pin and 72 pin, memory had to be installed in pairs. If you have multiple sets, you can try each set by itself to see if the problem clears. On some computers, there is "On Board" memory which is soldered to the board. If this is the case, you can remove all of the add-on memory chips.

      If this fails to determine the problem, you are pretty much down to the Video Card, power supply or Motherboard. If the Video card has just been changed, that is the most likely suspect. Contact the manufacturer for their advice.

      If the power supply voltages get out of the correct range, this could cause components not to work properly. You will need a professional to test the power supply voltages. See Power supplies for more on that.

      If it is the motherboard, this could be the CPU (Processor) or jumpers. If you have not changed any of this, it may be time for a new motherboard.

      This could be as simple as having the Mouse connector plugged into the Keyboard connector and the keyboard plugged into the mouse connector. On many machines these are both PS2 connectors. So that is real easy to do.

      If the keyboard is connected properly, the keyboard is possibly the problem. Try connecting another keyboard to the computer and/or connect that keyboard to another computer.

      If that fails to resolve the problem, you may have a defective Keyboard controller. Since this is a part of the motherboard, this can justify a motherboard replacement.

      If this occurred without any physical change in the computer, this could be an impending or actual failure of one or more of the memory chips. It could also be corrosion at the memory connectors.

      Physically remove the memory modules and reseat them. This will often improve the connections.

      Memory of the SIMM (Single Inline Memory Module) whether 30 pin type or 72 pin type, are almost always installed in pairs. If you have multiple pairs, you can remove two at a time. The receptacles are numbered from Zero and up. If you are removing modules, you normally must move all modules up so the empty ones are at the end.

      Reboot the computer to test each set of memory modules. Hopefully, this will indicate which module is failing.

      If you computer has "Onboard Memory" you will have to change jumpers on the motherboard to disable this memory. See the user manual for the motherboard for information on doing that.

      Many computer store can check the modules on a tester. This usually won't cost much, if anything.

      If you have recently added memory, you could have mixed types or the wrong type. EDO memory will not work in older machines not designed for it. You cannot mix EDO with non-EDO memory modules although they may look the same. There is also the parity-Non-parity issues. Normally you must have all of the same type.

      The light on the floppy drive(s) should come on for a second or two then go back of. The A drive light should come on again during Boot if the boot sequence in the BIOS setup is set for A drive as the first boot source.

      If the light stays on for either floppy drive, it usually indicates that the 34 pin connector is connected backwards. You could expect this if the computer had maintenance on the interior just before this began.

Once the P.O.S.T. completes you may get a message that there is a configuration error. This is reference to the BIOS CMOS settings. The equipment found must match what is listed in the BIOS Setup. If they do not match you will usually get a warning and a choice to:
Continue by pressing a key, usually F1 or F2
or
Enter the Setup by Pressing another key usually DEL or an F1 through F10 key.

You usually can continue with the boot. Unless this is an equipment failure, it may have no other impact the computer operations.

Among the items that can trigger this are:
Floppy Drives. The designation and size of the Floppy drives, A and B must match what is on the machine. The designation as A or B is determined by the Floppy Drive connection cable. Which ever drive you have connected to the A part of the cable must be the same as the BIOS setting for A drive.

The installed Memory must match what the BIOS says it is.

The Hard drive parameters must be correct or the setting must be "None".

      In some installations, two other files could cause problems:

      This could be a device failure (dead hard drive) or a configuration error.

      To check or change the CMOS configuration, you must run the BIOS Setup Utility. Many brands of computers use their own method for activating this. Most common computer use the Del Key during startup. Some computers display how on the screen during startup.

      The normal startup sequence is A, C. That is A drive first, then C drive. Almost all computers have the option of C, A which prevent booting from a floppy unless the C drive fails or does not have boot files set up on it.

      If you are trying to boot from a Floppy disk, there is the possibility that the drive itself is defective. See:
Floppy Drives by J.T. Murphy.

      In almost all of the following you will need a boot disk (especially if the computer won't start).

      As the computer starts, when you see "Starting MS-DOS" or "Starting Windows 95", press F5 (you can press F5 just before those messages are displayed). This will bypass the config.sys and autoexec.bat files.
You should get the C:\> Prompt.

      If you get the C:\> Prompt, these core files appear to be working properly. You can go to Configuration Files problems.

      If the boot fails, boot with a boot disk. Making sure that the boot disk is exactly the same version of DOS that the computer is running on, from the a:\> prompt, type:
sys c:
In a moment you should see "System transferred". Try to reboot the computer without the boot disk. Did this work. If so, you problem may be cured.

If the computer still hangs up, boot with a boot disk again. Type:
dir c:\dblspace.ini /a
If you are running DOS 6.22 this will be
dir c:\drvspace.ini /a

If you find a file there, Doublespace (or Drivespace) is trying to, or is being loaded. Type: attrib -r -h -s c:\dblspace.ini
or, with Drivespace: attrib -r -h -s c:\drvspace.ini

Next type:
ren c:\dblspace.ini c:\dblspace.in_
or, with Drivespace:
ren c:\drvspace.ini c:\drvspace.in_

      Now remove the boot disk and try to start the computer on its on. Since Doublespace (or Drivespace) will not be loaded, you will not see what is normally on your compressed drives. If C drive is compressed, what you will see as C drive is the real C drive.

      There also may not be a command.com to load. But if the boot goes further than it did, the Compressed drive files are probably the problem.

If this is not the problem, return the INI file by typing:
ren c:\dblspace.in_ c:\dblspace.ini
or, with Drivespace:
ren c:\drvspace.in_ c:\drvspace.ini

then
attrib +r +h +s c:\dblspace.ini
or, with Drivespace:
attrib +r +h +s c:\drvspace.ini

This will return the compressed drive(s).

      If this does not remedy the problem, run SCANDISK from the floppy disk. If the drive has defects, if can lose pieces of the boot files and cause hangups. If you cure whatever problem there was, you should also run scandisk as there may be a reason the problem occurred.