I have random shutdown issues with my system - and it's due to the storage drivers
. I reported the bug to Microsoft and we worked all the issues with the exception of my storage drivers (my RAID card won't have Windows 7 drivers, so I'll have to install a new RAID card w/Windows 7 support).
Sleep operations will generate the random shutdown with the symptoms that you've described. The Microsoft rep stated that there was a very specific section of the driver
's code that controlled this behavior, and that it was a known issue with Vista drivers on Windows 7 systems.