We have a computer thaty keeps going into hibernation despite resetting it. We think its possibly the video card. Any SUGGESTIONS?

*edit* Actually, it just shuts down. I THOUGHT it might be a power supply issue. It is turned on and will stay on 20 minutes then shut off. She will turn it back on and it will stay on.

*edit....again* OK. She says it has done this several times this morning before I arrived. Now its not even staying on 20 minutes. ONE thing she did mention was that it was doing it when she was in Outlook DELETING spam. I don't think that's an issue but figured I'd make mention of it just in case. But she did say that eventually it will stay on. Thoughts anyone?
What is th emake/model of the computer and the make/wattage of the power supply (it should be printed on the outside of it). How old is the macine?Dell Optiplex GX270

approximately 2.5 years old.

Not sure of wattage....210 I believe. I'm having an off day and can't find it.Well the mind readers are having an off day as well and can't find it either...The are small 200-250 watt units.

Turn the machine on and leave it in the Bios/setup screen. This will be before WINDOWS even loads, so no settings there will apply. See what happens and how long it takes.

Replacement power supplies must be ordered from Dell or a specific third party manufacturer. You cannot just go down to the local computer store and get one as the connectors and the size are Dell specific.Thanks for the help GX.