Internet connection problems with a new computer?

[Vi3nc6en0t]

We have this wi-fi router which was connected to it via an ethernet cable which connected it to the internet. Recently, we got a new computer and plugged it into the router as well. After all the set up processes, the new computer was successfully able to connect. However, when we plugged in the other one, it didn't. Help? Anyone? Steps would be greatly appreciated.

Thanks in advance~
They're both desktops and they don't have wi-fi cards. ._. The one that can't connect is running Windows XP and the newer one has Windows 7.

[Luke]

Use process of elimination. First switch the ethernet cables to make sure its not the port. And then run the troubleshoot program. And then if that doesn't work then try to connect it using wifi.

[Mike M]

Diagnosing network problems is always a bit tricky, but there are some simple ways to determine where the problem lies.

First we want to verify the computer can communicate with the router properly. The router will assign the computer an IP Address if it's able to communicate. To check your IP Address, open a command prompt (Start > Programs > Accessories > Command Prompt) and type ipconfig.

If your IP address starts with a 169, then your computer and router aren't talking. To fix this, I would first try restarting both the PC and router after a 30 second power off. If the problem persists, replace the network cable. If the problem persists, swap ports on the router. If the problem persists, reply here.

If the IP address does not start with 169, then the IP Address listed was given to it by your router and you know communication between your computer and router are working properly. Which means the problem is between your router, and the internet. Restart the router and your modem. If that doesn't solve it, contact your ISP (Internet Service Provider).