If you are running on Windows 2000/XP/2k3 you can check this.
Copy the following into the run command
Windows 2k
code:
notepad c:\winnt\system32\drivers\etc\hosts
Windows XP/2k3
code:
notepad c:\windows\system32\drivers\etc\hosts
The last line you should see should be 127.0.0.1 localhost.
If it isn't I suggest removing everything else unless you are on an internal network that uses a proxy to access specific websites.