Something is wrong with my internet..hacked?

The first thing I noticed is that my eBay settings had been changed to search international listings only? I still have not figured out how they got changed or how to change them back. I don't know if the eBay stuff had anything to do with the next problem but all of a sudden all those anti virus programs wanting you to buy their product started going crazy (more than normal) saying I had someone trying to transfer files from my ip to another ip address. I never even pay attention to those because I figure they are just trying to get me to pay for it. BUT now I try to get onto my internet through both google chrome and through internet explorer and the internet window pops up then about 2 seconds later just closes...its not my internet connection its my computer itself. Anyone have any idea about what's going on? Please help?