here is a post by me.
i've had problems like this myself, not as bad as you're describing, but maybe this will help.
all windows versions run many useless and sometimes harmful programs at startup since the moment it's installed. i still use 98, so i'm not sure how this works for other versions, but typing msconfig in the run box on the start menu, and clicking on the 'startup' tab brings up a nice list of startup programs in the registry. go to a site like
http://afsg.whatzit-inc.com/pc_performance/tasklist.htm and look up anything that looks suspicious or just inexplicable, and find out if you'd be better off without it. that solves most of my crashing problems.
get a program like adaware or spybot or the like.
http://www.lavasoft.de/ that generally clears out a lot of additional crap you don't need.
umm. if it's a virus i don't know. i sometimes get trial of norton when they come out with a new version.
http://www.norton.com/ i've never had a comp that was virus infected. i'm not sure what to tell you there. o.o
ok that's all.