Download, install, update and run the latest version of AdAware
Do not allow them to sell you the paid versions. The freeware version works just fine and there's other freeware for the additional protections you gain in their paid versions.
Then download, install, update and run Spybot Search and Destroy.
Read their tutorial carefully as misuse can cause serious damage to your computer systems.
Spybot S&D: http://www.safer-networking.org/en/index.html
One more that I would recommend is A≤ - Free from http://www.majorgeeks.com/download4281.html
Run it, click Search for Updates, then click Scan.
If the combination of those does not cure your problem you will need Hijack This.Hijack This
and a variety of other tools for malware and pestware. Download Hijack This from:http://188.8.131.52/~merijn/files/HijackThis.exe
and then go to the Blinking Computer directions on how to get help using it before you install it.
How to get help using Hijack This and get a team memberís assistance:http://www.bleepingcomputer.com/forums/How...s_Log-t956.html