Best solution when all else fails. Format c: and reinstall operating system.
thats my favourite.
But what you've gotta do is just remove all the adware and viruses b/c it sounds like you've got a lot. Norton scan, trend micro (free online scan), lavasoft adaware...there's tons of free adaware stuff out there just google it. And just know where to go, trusted sites and dont download and install everything you find. Be picky.
One last thing. Go to start>run>type msconfig Go to start up programs and remove all unnecessary programs that run at startup. *Warning* Only do this if you know what you are doing. If your using win2k, it doesnt come with msconfig, but you can download it.