Vista Business - Pentium D 2.66    1GB    350GB     Since I installed Vista SP1 when it was released my computer usually shuts down while booting, then restarts, shuts down, restarts.  It may do this four or five times before it finally completes the boot.   Then it may be ok for the rest of the day.....except.....occasionally, but not often, it will shut down for no apparent reason and reboot again.   I have another drive in this computer that has XP Pro on it.   If I disconnect the Vista drive, and hook up and boot the XP Pro drive, there are no problems, so it is in Vista and not some hardware problem.   Any one else have this problem?