Ensure you're logged in as an administrator.

Check the following location: C:\WINDOWS\system32\drivers\etc

If you can't access this folder, go to tools -> folder options -> view, show hidden files and folders, and ok it.

Inside the folder are a few files, the file you need to check is "HOSTS". Open this file with notepad.

The file should contain some information, in the form of comments, and the following line of code:

Code:
127.0.0.1	localhost
If it contains any other IP addresses and hostnames, delete them all.

If the HOSTS file was clean, then download and install Spybot S&D from here: http://www.safer-networking.org/

Run a full system scan and fix the errors it tells you to fix.

If the problem is still there after this, download HijackThis from here: http://www.spywareinfo.com/~merijn/programs.php

Make a folder in the root of your system partition (i.e. C:\hijackthis) and extract the zip file to this location. Create a shortcut from the hijackthis.exe to your desktop and run it. Do scan and save a log file. Do nothing else!. Next post up the contents of the log file here.