Have a look
The ones you want to look at are the anti-spyware programmes. Listed in Skidsy's original post. They are free. Run scans. (I use super antispyware
and have spywareblaster also installed.)
You may find that the pest is hiding in system restore. So one option might be to turn this off. Scan the PC and then turn back on system restore.
By turning it off you will lose all your restore points. Please bear this in mind.