try following instructions for troubleshooting this issue.
For Windows 7 or 8:
1. Hold down the Windows key and press R. (This will open the Run dialogue.)
2. Type cmd and press Enter. (This will open a command prompt.)
3. Type ipconfig /flushdns and press Enter.
4. Type ipconfig /registerdns and press Enter.
5. Type ipconfig /release and press Enter.
6. Turn off your Modem/Router and wait 5 minutes
7. Turn your Modem/Router back on, wait until it booted completely
8. Back on your PC, type ipconfig /renew and press Enter.
9. Type netsh winsock reset and press Enter.
10. Reboot your computer.