Virus

My computer has a virus... it causes windows to pop up. Seriously who gets a pop-up virus? It's like I just started hanging out on the internet or something. I did a virus sweep with AVG but I am not sure if it killed it or not. Nothing seems to be happening right now but I fear that it is secretly ravaging my computer without me knowing it, and one morning I am going to wake up and my computer with have exploded.

I want to reformat but I don't know how with this comptuer, this doesn't come with a disk... I think I just have to ask it nicely and maybe then it will reformat.