A friend's desktop is acting very strangely.

Working away normally, and the desktop shuts down without warning. Sometimes it happens during booting up.

The spooky bit is that when it appears to be off it switches on again even when he is out the room.

I looked at the power options, and they are OK. hibernation is off. power saving is only on the monitor.

Could this be a virus?

Rannoch

By desktop do you mean the screen goes black? Or do you mean you just lose the Windows desktop but other things remain visible?

Have you checked the monitor connections?

Check your Event Viewer via Administrative Tools.

Open the System as well as Application tabs and look for red X errors that coincide with your problem. Details here:

http://support.microsoft.com/kb/308427

Sorry, when I said desktop I meant PC. Nothing to do with the monitor.

When he is working on the PC, the PC switches off without warning.

On a number of occasions the PC has been switched off (manually - normal power down), only to switch itself on again later in the day.

The hibernation option is off, and the power saver only set for the monitor to switch off after 20 minutes.

Rannoch

Shutting down would generally be either an over-heating CPU or a failing PSU.

Turning back on would most likely be a BIOS setting. Either a Wake-on option or a Restart after power failure.

If the system is detecting the shutdown as a power failure due to heat then when it cools sufficiently it might restart if set to restart after a power failure.

Do you have a temp monitor on the CPU? If not here is one: http://www.stvsoft.com/

You can also get a PSU tester for a few dollars at most electronics stores.

Tried the suggestions, and the power options were off in the bios. Didn't appear to be overheating.

So, final act was to phone Dell. After a half hour call, they didn't know either, and its now on its way to the Dell mothership for repair.

Thanks for the assistance.

Rannoch

Thanks for the update and thanks.

Let us know how it comes out.