Wierd Virus?!?

Hello all!
I have what I think is a virus on my pc. Every time I try running a full system scan with my Norton 2005 software, the pc switches off. On restart there is no indication that a problem has occured( no scandisk tries to run).The pc acts as if I have shut it down. I have downloaded and tried several other anti-virus software only to have the same problem. It has been suggested that I have a virus that shuts my pc down on detection. Is there such a virus and if so how do I rid my pc of the bastard thing? It was also suggested that perhaps the problem is in my registery, so I installed and ran Registry Fix. It discovered over 800 problems and repaired them, but I still can't run a full system scan with my anti-virus software.
Please help
Cheers!
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