I've been experiencing this strange problem lately, basically i leave my desktop PC running all the night and when i come back in the morning i have a black screen and i can't bring windows on. Today i did some investigation using the windows reliability monitor and i've discovered that windows never hanged, it was me that always shut it down trying to get things back working (i always keep the power button pressed to shut down the PC because i have a black screen but the PC is running). This is the log from this morning
The previous system shutdown at 09:34:59 on 25/06/2012 was unexpected.
So this might relate to my video card, i have recently bought a AMD Radeon 7950 card from Sapphire, and i connect it to a 24 inch samsung monitor with a HDMI to DVI cable. When i used the standard VGA cable and didn't have the new card i'd never had this kind of problems.
Of course i have the latest drivers :)