Yesterday I laid down to wake up and find my computer shut off with a blinking yellow power light. Ive removed all hardware that could conflict. I have had it for over 6 months now no problem. I thought it may be my power supply so I went out and purchased a corseair 600 watt power supply. It is a dell optiplex gx280. 2 gigs ram the power supply I said and an xfx radeon 4550hd graphics. OK when I go to power it up system fan starts external fan starts. Hard drive starts. Monitor light turns green then bam it shuts off. Some starts are a little longer lasting than other times. Usually it just barely powers on then shuts off. What I described as hearing everything run then instant shut off last for about 3 to 4 seconds. I switched the cmos battery as well. ANY feed back please. I know its got to be a semi easy fix. Unless my mobo is shot. Like I said Ive stripped it down to just power and mobo and I get the same result. PLease help Thanks Josh.