My daughter & I just went thru this same problem.

my puter /hardrive finally crashed so I had to get a new one and start fresh.
daughters is still functioning she reinstalled win XP for now.
I had reinstalled it on mine and was good for a week or 2 but then constant blue sceen every time. I think I messed up when I deleted some of those bad /virus files- prob why I had a total crash later.

I ordered some linux products from Amazon - Ubuntu & Kubuntu {free from the website {Ubuntu & Kubuntu } or you can get them from Amazon.com {9.95} you can run them from the DVD to try them out - or install them.
plus you can do it as a dual boot system and still have your windows for certain programs.

right now they don't "see" my wireless connection, so I'm using windows for online til I get that figured out.
but if you have a direct modem connection or cable network they will probably work fine.
Linux is much less susceptible to hackers and viruses. AND pretty much FREE- because it's open source.

you can also try downloading - stinger - a free virus product
I read that sometimes one product will not catch all viruses so a variety is needed to keeep a clean system.
the free trial of bit defender is what finally removed the ones I had.
netsky A B
bugbear
some that i can't remember.

there is stand alone removers for specific viruses on the AV websites- bit defender website and pcillin? and mcafee site- i think too. explore on those.

do you run spyware /adware too?
spybot is a good one- it found more than spydoctor on my machine

I suggest
clean up hardrive
go thru and delete/remove any old programs that you don't use.
defrag hardrive if needed
then do full scans with spyware/adware scanners & a couple of AntiV scanners.