Computer boots up fine. But before we can do anything it just shuts off completely. No error message nothing. Tried booting in safe mode and it does the same thing maybe takes a few minutes longer but not much. We have taken the cover off and cleaned everything out...tried changing the power cord ...changed monitors...we did get time to do a system restore nothing...Now we can't get it to stay up for more than 10 to 15 minutes at a time. does anyone have any other suggestions???