Help! My screen is loading up all black except a fake antivrus!

I'd have explained in the itle, but it was a little hard to. In any case, heres the problem:

I was surfing the web looking for a video when I found a supposed copy of t. It was set up to look like a youtube video, so I clicked it. Instead of running, it said I need to download it, so figuring it nwould be safe to just run instead of save it, I did.

 

I started getting pop ups for fake antivirus programs, so I figured I'd messed up and downloaded something pretty bad. Figuring I could deal with it in the morning, I turned off my computer, and went to bed. WHen I woke up and logged onto my account on my computer, I heard a woman speaking in- German, I think- and then I saw another fake virus-stopper scanning my computer, except this time the entire screen was black. No shortcuts on my desktop, no backround picture, no toolbar at the bottom of the screen, and no vista gadgets, and I couldn't even close the  program! I had to use Taskmanager to close the program, get onto norton and navigate my way here.

 

Is there anyway to fix it? I don't want to tell everybody else who uses the computer that they have to navigate with taskmaster from now on!