then go Start then Run in XP - (Windows key plus R in Vista and Windows 7), then type in the following, including all the spaces:- cmd /k ping www.yahoo.com -- then press Enter and from the black form that shows up, see if it will ping the IP. Type exit to close the black form.
If you can ping the IP and you still unable to access the internet, try the following:
Open Internet Explorer by clicking the Start button Picture of the Start button, and then clicking Internet Explorer.
Click the Tools button, and then click Internet Options.
Click the Connections tab, and then click LAN settings.
Make sure the "Use a proxy server for your LAN" check box is unchecked.
Even if should have internet connection again, run through Step 1 of this malware guide to make sure it is not malware causing the problem.http://www.tomshardware.com/forum/248626-45-simple-free-guide-removing-malware