Question Old System not powering on when CPU power is connected

[Luka_P]

Hi,

I have this issue with an old System where the system fails to power on when I have the CPU power connected on the motherboard.
Without the CPU power connected the system powers up normally (doesn't post obviously) but the fans spin and the motherboard has power etc.
When the CPU power is connected the fans spin for a split second and then everything shuts down.
I believe the PSU is shutting down on purpose since a red light is showing on it and trying to power on the system again doesn't work until I turn off the PSU switch and turn it back on.

I have browsed for a solution to this issue and everything I found suggests it's either a dead PSU, CPU or Motherboard.
The problem is that I have tried a different CPU, different PSU and different Motherboard and still always the same problem.

I have no idea what else to try.

The system is and old DDR2 system with 775 socket.
Both CPUs are Core 2 Quad.
One of the motherboards is a gigabyte board and the other is ASUS P5QL-E

Can anyone suggest what else could be wrong?

Thanks

 

[RememberThe5th]

What about ram?
Thats the only thing you havent removed..

 

[Luka_P]

What about ram?
Thats the only thing you havent removed..

I have tried to run it without any ram installed. Same thing.
CPU power connected: split second and complete shutdown,
no CPU power: everything powers on with no POST and idles.

I even tried switching ram sticks to different ports, try with just one and switch, etc.
Nothing seems to be working :/

Same thing with GPU. doesn't seem to make any difference

 

[RememberThe5th]

What about standoffs and cpu cooler?(brand and model of the cooler)

 

[Luka_P]

What about standoffs and cpu cooler?(brand and model of the cooler)

Sorry about late reply, was away for a while.
The standoffs all seem fine. I reseated one of the motherboards twice and once the other. Checked them each time and they all look fine.

The cooler is an akasa simple cooler for intel LGA775. I'm not sure what the model number is because it's not even on it's original box.
It's a very simple cooler that seems to work fine. I tried turning on without it as well. same exact result.

I was thinking that maybe there is something wrong with the case that I'm missing?
I can't think of anything else that it can be. I will try setting up the motherboard, cpu and psu to run outside the case maybe I get some results this way.

Will report back.

 

[RememberThe5th]

What about another PSU? Which current one do you have? (Forgot to ask)