Errrr....

[Bond]

I'm going to asume you currently run none of this, so to get started.

Windows AntiSpyware
If you ask me this is currently the best free spyware program out there. Download it and then run a deep scan and see if it finds any spyware.

AntiVir Personal Edition
This is my favorite free anti virus program. Download it and then scan your entire computer for any viruses.

Windows Update
Make sure you've downloaded all of your windows updates as well.

After you run these two programs go to My Computer -> right click on C Drive -> Properties -> Tools. Run both error checking and defragmentation.

So after you've run those four programs see if it's fixed your problems and if it hasn't come back and I'll think of some other generic things to do.