Perhaps this tip might help:
Try the following:
Open Command Prompt as Administrator (click Start, type "command prompt" in the search bar, right-click the Command Prompt icon that will appear and choose "Run As Administrator" from the menu).
Enter the following commands followed by enter:
netsh I i r r
netsh winsock reset
You will be resetting the tcp/ip stack and the winsock catalog. You will need to restart afterwards. That usually fixes the problem. Follow this up with a malware check. Something has messed with your networking stacks.
Are you running multiple anti-virus programs and/or firewalls? You should only be running one at a time.