i think you may need a new power supply i had same problem the same time i bought plane scape torment a while back.

put your hand behind your psu fan eg behind top part of pc case (assuming your case is a tower one) and see if you feel any air getting sucked in and if you dont feel a decent amount getting sucked in by your psu fan thats the problem. your pc will probly be shutting down due to psu fan failure so the psu heats up to much and bamm it shuts down.

am i right in thinking your pc wont let you turn it back on as soon as it shuts down? if so its your psu