How can I tell when my PC was restarted?

My office PC restarts every Sunday at an unknown time for unknown reason. I wish to know when my PC restarts and most importantly reason for which it restarts. I suspect that there is a third party install that force PC to restart.

Could you let me know how to determine the date and time when the PC was restarted? My OS is Windows XP SP3.

Thanks.

To help diagnose the restart, what you should first check is Event Viewer.

Just enter eventvwr in the run dialog (which can be called by pressing Win + R).

Under Windows Logs > System look for events from the "Kernel-Power". This will also show if the system unexpectedly restarted by a blue screen and show events prior to it.

If it was a blue screen you can view the BSOD using BlueScreenView.

If you open a command prompt and type systeminfo, the command will spit out some data, including when it was last booted.

More info here.

Windows 7, open up a command prompt and type:

systeminfo | find /i "boot time"

You will see a single line showing when the computer was last booted:

System Boot Time:          2/26/2013, 4:33:35 PM

OR

Windows XP open up a command prompt and type:

systeminfo | find /i "system up time"

You will see a single line showing how long the computer has been up:

4 Days, 15 Hours, 31 Minutes, 36 Seconds

It's likely it could be Windows Updates set to install on a Sunday night. Open Windows Update from the start menu and check the settings for when it is set to restart.

net statistics server

Entering this in the command prompt will give you the time the OS was started. From there, you can cross-reference with the Event Viewer to see what occurred before this time.