What is infecting my computer??

I can't figure it out. I can't stop these BestOffers and webtopsecurity.com pop ups. I tried deleting the BestOffers from my Add/Remove Programs and it wouldn't delete. I just took me tot he website and gave the same instructions. And the webtopsecurity.com keeps telling me my computer is infected and suggesting programs to help that I know are just more spyware. Also there are the carnival pop ups that give me Casino stuff. They won't go away. I've tried a few of the spyware removers on here but nothing has worked so far...what would you suggest?