PC is shutting down after few seconds

hello,

I'm glad I am already a member of this site.
I am repairing my PC at the moment. when I turn it on after a few seconds it shutdown. I changed the PSU, still the same problem. I remove the RAM and it has long beep it means my mobo is working but still after few seconds it shutdown. any suggestion?
 
PC is shutting down after a few seconds

Hello,

thanks for the response. sorry i,m still new on this site. i don't know where to post my reply. by the way here are my computer specs:
CPU INTEL '04
PENTIUM
8 05 SL8 ZH MALAY
2.66 GHZ/2M/533/05A
Q621A147
PSU P4-500 W
RAM DDR 256MB
Motherboard ECS 865G-M8 REV:1.0
15-S04-011004
Video card Built-in

Hoping for your suggestions on my problem
 
It could the CPU fan. Make sure that it is connected properly, and that it isn't clogged with dust.
Make sure that all cables are connected properly, especially the cables connecting the motherboard to the PSU(2 cables usually).
After you have done this, turn on your PC, and check if the fan(s) turn on.
Also, the motherboard might be touching the case (not where the screws are), causing it to short-circuit.
 
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