My PC shuts down automatically at night after 1 hour or sometimes 3 hr. I dont know why. It might not be temprature or PSU issue because i use PC for more then 5-6 times during daytime continues but this shut downs happens every night.
IN Power Setting Mode >> Going to Sleep << Disabled.
not necessarily a "problem" as the power saving settings in Windows 7 are much more advanced and offer far more options then XP. So same recommendation here...check your Windows 7 power settings first.