performance?

I have an AMD Athlon 64 X2 dual core 4200+ 2.2G with 2G Ram. it has run fine up till 2 months ago when my daughter pulled up a website that had a virus attached. I have run AVG, AVAST, Ad-Aware, Spybot, CCleaner, nCleaner, Advanced System Care, and defragged over and over. These found 2 viruses and supposedly cleaned them. AVG seems to constantly find spyware. It runs very slow right now, freezes up a lot, which it has never done before.
Any suggestions on how to speed it back up to parr?