Computer idle for a time it shuts off.

hi
i was working on some files then i left my computer on as it is and went out side for small work but when i come back my pc got shuts off so i check for that i observed when Computer gets idle for a time it shuts off.why this is happening ?please help
thank you

It does sound like a power problem also check for power supply cooling problems check that the air vents are clear and fan running proper check power settings for fan use application to check fan speed mainly benchmark application...use Riva tuner

This problem looks due to power supply settings In the Power Options dialog box, you set options for a power scheme. Windows XP comes with several preconfigured profiles. I've shown the Normal profile for my laptop here, but you can easily create custom profiles that fine tune the properties for your particular circumstances. You can create a new power scheme by clicking the time settings you want, clicking Save As, and typing a name so check here for more http://www.microsoft.com/windowsxp/u...02march25.mspx

Due to power supply settings setting you have set computer get in to idle mode with shutdown screen but then i think due to some third party application or virus computer not able to maintain its status so it get shut off so better to check for virus and overall computer performance and hardware...