Are there some websites that you are unable to open in a browser from your computer?
One possible reason is that those particular websites are listed in your Windows hosts file. A spyware program such as Spybot Search & Destroy inserts a list of entries that might include those unreachable websites. A recent peak at my Windows hosts file revealed close to 8,000 listings inserted by Spybot! Those websites listed were all mapped to the incorrect IP address 127.0.0.1.
Type the following command in the Run Window to view your hosts file:
cmd /k notepad c:\WINDOWS\system32\drivers\etc\hosts