can't change search engine

I got a little bug in my puter that hijacked my search engine to begin 2 search from msn search of course i freaked out and downloaded 14 different spyware detectors and all say that the threat has been removed but now i can't change my search engine back to msn search, when i click on customize it opens a little box that shows msn search but doesn't give me the option to customize my search engine it just opens my webpage to msn search. I have tried differen't approaches but all have been unsuccessful. maybe someone on here might have a helpful solution that I haven't tried. thanks.