i had the same problem with vista doing that... but it turned up being the crappy nvidia graphic drivers... on about 11 different systems after the first install and then it was raid drivers on 3 of the the intel boards i put in... finally got got some updated drivers a month later and was able to sell the rigs but i know your dealing with a different os so i wish you luck.... cause anything could cause that problem , mb , memory , psu... i even had a dvd burn trying to hang at shutdown and cause the weird problem good luck