Please help me!

My computer is been acting weird for a couple days by now and im not sure whats going on, I've scanned it with the antivirus and found like 3 disgusting trojans and it deleted them but my pc is still acting weird, sometimes when i open the browser it closes by itself automatically, sometimes a weird advertisement window appears by magic, and my pc is so slow sometimes that is freaking me out!, please tell me what to do...im using windows xp, I have kapersky antivirus, spyware search & destroy and ad-aware as well but nothing seems to work with this problem :cry