Power Supply powers off and powers on again repeatedly

[STUBBY23]

Hi guys,

I have a problem with my Shuttle SZ77R5.

1) When I hit the power button, the PSU fan spins up (the GPU and exhaust fans spin as well) then you hear that familiar 'click' sound of the power to the PSU being cut off.

2) My system goes through 5 or 6 of these PSU power on-off cycles. Sometimes the computer boots up after these cycles. Sometimes it doesn't.

I've been using this system for a couple of years now. What could be the problem ?

Here's my config for reference -

Intel Core i3 3220
Samsung 840 EVO 250GB SSD
WD Green 2TB HDD
EVGA GTX 750 Ti
G.Skill 2 x 4GB 1333MHz DDR3 RAM
Shuttle's own 500W 80+ Bronze Power Supply

I have never had any problems with temperatures (the hottest component in my system is usually the i3, at about 45 degrees celcius) and I have never overclocked this system.

Any thoughts guys ?

 

[LTC8K6]

It's probably the power supply.

Clean the dust out of the case and the PS, and make sure all of the cards, ram, connectors, etc, are all well connected or all the way in their slots.