Posted 16 May 2011 - 02:36 PM
First, I would check out the event logs to see there are any clues there. There should be some kind of entry there. Even if it doesn't capture the faulting event, it might give you some kind of indication of what is going on before the event.
Your description of the event also makes me wonder if the system is rebooting during the night. Is this the case? Are there any scheduled events that happen every night at the same time that might be causing a crash? Anti-virus scans, backup routines, etc...? Maybe you could change the times to run right after closing so that you could login remotely from home or something and see what is going on before you go to bed at night.