Give us a HiJackThis log and we can better see what we may need to look for or where to look.
Do these steps first;
Make sure you have NO startups disabled via msconfig.
Go to start, run and type in msconfig. Go to the start up tab and make certain there are checkmarks in everything there.

Enable Viewing of Hidden Files and Folders

Download HiJackThis

Create a new file folder;
For Windows XP users, here is one way to do that:

To create a new folder:
Click START > My Computer > Local Disc C: > Program Files
Now, RightClick on an Empty Area and select New > Folder & name it HijackThis and Click ENTER.

To Extract HijackThis:
Now, RightClick your HijackThis ZIP File and select Extract All > Next > and browse to your newly created HijackThis Folder (C:\Program Files\HijackThis)and click Next.

It is EXTREMELY important that HijackThis be properly located before you use it!
Now with ALL other programs closed including Spybot Teatimer, browsers, mail programs, AIM, etc., run HJT and save the scan as a text file and then post it here. We will take a look.