My Computer Won't Connect to the Internet
Dial-up Problems
Dial-up problems are often the easiest of connections to diagnose. If your computer won't connect to the Internet or drops the connection frequently, it's usually the service provider, not your computer. However, there are steps you can take to ensure your PC is not the culprit.
Ensure you have no viruses on your system that are interfering with your Internet connection by scanning your PC thoroughly. See the Removing Viruses guide if you need help with this.
Make sure you don't have spyware that is so greedy for an Internet connection that it begins hogging the instant it detects any sort of modem activity, which could be messing up your dial-up. Run a spyware scanner, and see the Dealing With Spyware guide for help.
Check the obvious. Is your phone line firmly plugged into the wall and the modem? If the modem is pass-through, is the phone line in the "to wall" jack and not the "to phone" jack? If you have an external modem, is it powered and ready? If internal, is the card firmly seated in the PCI or ISA slot?
Try a different phone number provided by your ISP, if you have one. Perhaps one number is overloaded with connections and is beginning to lag.
Ensure you have the latest drivers for your modem.
Make sure your dial-up software has the modem properly configured. Incorrect detection of the modem, improper initialization strings and other programs attempting to use the modem will stop it from working correctly.
Turn off voicemail, call waiting and other phone options that could interfere with the dialing process.
Make sure no one is using the phone, or there is not a phone off the hook somewhere.
Make sure the phone line you are using has a dial tone, and that the line is free of static and noise. If you hear something strange in the line, call your phone company.
Clear your Temporary Internet files and cookies.
If you have AOL, try clearing the AOL browser cache and uninstalling the AOL adapter, then running AOL again. If you have a newer version of AOL (8/9) then run the Computer Check-up. Amazingly it does a decent job of fixing most AOL related issues.
Broadband or LAN Problems
These problems are a little harder to diagnose, because a host of factors can cause a LAN or broadband connection to fail. LANs are usually less reliable than individual broadband connections, depending on the topology of the network you're connected to. Here are some things to check:
Check the LAN card in your computer first. Are the green activity and connected lights on? If not, then: a) the card is not seated properly, b) the cable is bad or loose, or c) the connection that should be providing power is down or missing, which usually means a bad router, switch, or hub.
Check the status of the network connection under Start->Control Panel->Network Settings or Connections. If the IP address is an automatic private address, reads 127.0.0.1, or is missing, then the network is not assigning you an IP address for some reason. There are a few ways to remedy this. In Windows XP, try clicking the "Repair" button, restarting the computer, a combination of connected and disconnected cables and restarting the PC. In Windows 98, try the "Repair" button if you have one, or simply restart the PC. Make sure the connection is set for an automatic IP address if required, and in fact, make sure all settings are correct, according to the setup your network or ISP gave you. If you don't have this information, call them. Try default settings if in doubt.
Call the network office or ISP and ask about the system status. The server might be down for maintenance, network problems or overloaded. If this is the case, simply try again later.
Some networks will turn off your connection if you have a virus on your computer. Check with the main office to ensure you haven't been shut off for file-sharing, exceeding bandwidth or virus propagation.
Speaking of viruses, make sure viruses or spyware aren't lagging your connection so badly that it appears you cannot connect.
Check to see that your computer meets minimum system requirements for the network or ISP.
If you've isolated your computer as the problem, then fix it using one of the techniques suggested above. If it doesn't appear to be your computer, then call the ISP or network office and engage in troubleshooting. The network may just be down. If it's night or a weekend, and there is not 24-hour support, simply try again later. The problem may resolve itself on some self-repairing servers.