start up instant shutdown issue

Lately i went to turn my pc on and it would light up and almost instantly shut back down after a few trys it turned on and even stays on, so its hard to say the power supply is the problem, what else could be the problem.

I have not opened it up yet to check if anything burnt out a bit.

When he says dust your interior he doesn't mean get out the dusting cloth and feather duster. He means blow the dust out not with your mouth with a can of air. Don't use a vacuum either.

http://www.technibble.com/how-to-clean-the-inside-of-a-computer-case/