Hmm i had a problem like this once on 2 machines. The first machine PSU wasnt providing enough power & just cut out as soon as everything started to power up. The Second was a faulty PSU to Motherboard connection.
So have you tried any or all of these.
1) Replace PSU
2) Replace GPU
3) Change or swop memory slots
4) Remove all power connectors to none critical hardware needed to boot up
5) Checked to cpu for over heating
6) Replaced the Thermal Compound on the cpu with a fresh batch
7) Make sure there's no phisical connection from your motherboard to the case (I had a screw under mine once, fractions away from blowing my board completely)
If you have done all these & it still boots up & then shuts off after 5 seconds, i can only think a motherboard problem.
When you boot up, does anything show on the screen before it turns off or does it trigger your monitor to fire up or dosnt it get that far?
Originally Posted by Slaymate
If the power switch is shorted or stuck it will power off.
You can test this by un plugging the lead to your pw sw lead from your mobo & put your reset sw lead in staid & push it in to power it up.