Try restarting your router, releasing / renewing your IP and restarting the PC which will probably fix it - also flush your DNS.
1. Click Start, Click Run, type CMD and press entre - black DOS box should appear
2. If you're on any other drive than C:\ type C:\
3. Type IPCONFIG /RELEASE
4. Type IPCONFIG /RENEW
5. Type IPCONFIG /FLUSHDNS
Remember to restart router as well if possible if you're on a network and other PC's are working then the above should probably fix it.
M