Robin Hoods Playground

How do i get rid of a virus that poses as antivirus software? I downloaded a virus that poses as an antivirus that wont let me run task manager or real antivirus software. When I restart and get into task manager it shuts it off once it boots up. It seems to want me to activate it like I'm retarded. It won't let me turn off system restore either. Any ideas how I can get into safe mode or something to this malware down. I'm running windows 7. I have higher than average computer skills but this thing is tricky.
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Most of the major AV softwares have a boot disk option that will scan your hard drive prior to windows loading...
don't remember the specifics because it has been a while, but I would check into that...