did you have a look in the Event Viewer?
I have had my computer cycle and shut down many times, and usually it was due to two conflicting anti-virus and spyware software running at the same time, like McAfee Anti-Virus and Webroot Spyware.
Am now using AVG free, and find it good for all my needs, except that I must do a manual computer scan to catch malware and spyware warnings, some of which should have been caught.
Out of the blue, with ONLY AVG running, in the middle of typing Word documents, or even surfing the web, the PC begins to cycle for 15 - 20 seconds and then shuts down. It starts right up, and runs many hours with no problem, then all of a sudden, the cycling starts again, and down it goes.
Any ideas? I have checked for automatic downloads that may conflict with Windows vista, and have checked the Windows site to be sure I have all the needed security downloads on board.
I can do a system restore moving back to a recent check point, but before I do this, I wondered if anyone else has had a similar situation.
Thomboy

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