Think I had a virus or trojan
I had the blue screen deal while back and had to format the computer and Windows XP reinstalled. It wasn't a virus it was I would install things, find that I didn't like it and then delete it which left the registry in shambles.
My computer guy recommends CCleaner.. it's free and they keep it updated.
CCleaner
Optimization and Cleaning
http://www.piriform.com/ccleaner/update?v=2.35.1223&l=1033