Why does my computer reboot by itself

Question

My computer sometimes reboots when I'm not near it, usually sometime at night or early morning.

It happens ay completely random times, not every day, not the same day of month or day of week and not at the same time of day - sometimes it happens in consecutive days sometimes it doesn't happen for over a week.

It never happens when the computer is in use, usually it happens in the middle of the night but it can happen during the day if I'm away from the computer, I've never seen a message saying the computer will automatically reboot (except after windows update - and that's not the case here)

The system is running Windows Vista Ultimate, this computer is at my home - it's not a part of a domain and there is no domain controller on the local network.

I believe Windows Update is not involved because after the reboot available updates are not installed, windows update is set up to download all update but not automatically install them.

I've used the event log to try and find the problem, I've found when the computer rebooted but there was nothing in the system or application logs right before the reboot (actually, there was nothing but standard notifications that happen all the time for hours before the reboot).

There is no special hardware in this computer, there is a lot of software installed most of the time MS Office 2007, Visual Studio 2008 & 2010, iTunes, IE and FireFox are running (as well as a lot of small utilities), any software that has auto-update is up to date (including Windows itself and all the programs listed above).

(the "small utilities" running right now, based on the notification tray icons, are: dropbox, tortoiseHG, JungleDisk Simply Backup, MS security essentials, USB safely remove, "Control Center 3" and "Status monitor" from the brother MFC-250C printer software, Crushplan and Windows Clipping)

The computer's power cable is connected to a surge suppressor, the same model of surge suppressor as the rest of the electronics in the house, I have not seen any evidence of power interruption in any other device. the weather as been very "good" this winter (almost no rain or strong wind) and power has been stable.

This is very annoying since I sometimes leave things running overnight, does anyone have any idea how to find what causes those reboots?

Update:

Except for those reboots the computer is stable, there are no blue screens or anything like that.

Sleep and hibernate are disabled (there were problems with resuming from sleep - but I don't really care because that's wouldn't work with running things overnight anyway).

The overnight jobs are not intensive, and the reboots also happen when the computer is idle

Answer 1

Is your computer by any chance set to hibernate after x minutes/hours of inactivity? Perhaps the hibernation fails and makes your computer reboot instead?

If that's the case, the power settings should be easy to find in the control panel. There could also be some pre-installed 3rd party programs that handles power settings.

Something else you could try is upgrading your BIOS and drivers. I know some people recommend not fiddling with the BIOS at all, but there is often (if not always) a switch on the motherboard to set the BIOS to factory defaults in a worst case scenario.

Answer 2

Do you also have issues sometimes at bootup or an occasional freeze or unstable situation (bluescreen)?

I would then recommend checking the memory and cleaning the memory's contacts.

BTW, Memory is RAM in this case. Don't touch the contacts with your fingers.

Answer 3

The problem was a bad graphics card or a bad graphics driver.

Found out when one time the computer blue-screened and rebooted in front of me, I have no idea why the blue-screen details weren't in the event log.

I have since discovers the GPU fan malfunctioned so it may be related to GPU overheating - or it could be just a bad driver installation.