1. Have you tried re-initializing the modem/router like this? Turn OFF the computer, then turn OFF the router, then turn OFF the modem (if they're separate routers and modems), then wait ten minutes.. Now turn ON the modem, wait two minutes for it to reinitialize, then turn ON the router (if they're separate), wait two more minutes, then turn ON the computer.

2. Since you didn't tell us which operating system, IF you're using Windows XP, download the free WinsockXPFix tool from the link below. After downloading the took, run it to fix the network connection files.

http://www.majorgeeks.com/WinSock_XP_Fix_d4372.html

If you're using Vista, try the steps in the link below to do the same thing:

http://support.microsoft.com/kb/811259

Hope this helps.

Grif