First, if you haven't used the tool below, download, install, update, then run a full system scan with the free malware removal tool below.. Run it repeatedly, till it finds nothing.

Malwarebytes Antimalware

Once that's done, download the registry fix tool using the instructions below:

Go to the link below and scroll down to line 12 (left column) and click on "EXE (lnk and regfile) Fix for Windows XP" to download a reg file fix. Save the REG File to your hard disk. Double click it or right click it and choose "merge" and answer yes to the import prompt.

http://www.kellys-korner-xp.com/xp_tweaks.htm

Hope this helps.

Grif