hello, we can assume you are using xp? Can you post a hijack this log in this thread. It's a free tool to help experts here analyze what may be wrong.... the link for it is below. Before you do that though, download and run adaware and spybot... also below and free-use tutorial links on how to set them up......Here's how to post a Hijack this log here [and remember wait here for advice before you 'Fix' anything with it]
Run Hijack This from your Program Files folder
(NOT a temporary files folder) or you may loose the ability to undo any changes you make later using the Hijack This back-up feature.
Close all open windows/and any open web browsers and then open Hijack This. Click Scan. When the scan is finished (it only takes a second), the scan button will change to Save Log. Click on Save Log and then save it to NotePad. Click on Edit Select all copy and then paste into the thread.
DO NOT FIX ANYTHING YET;- Await further analysis here.