Question P5Q-E no video signal

[Automatron]

Dug up my old, dusty PC and tried to turn it on. No video signal. Unplugged everything non-essentials. Unplugged all RAM modules. Power on the motherboard (MB), CPU cooler works, power LED on and it beeps with the error code of the missing RAM. A good sign, it seems MB is not completely dead. Plugged one RAM module, unplugged GPU. MB starts but no beeps. It should beep with the "no GPU" error according to the manual, but it doesn't. Plugged two different GPUs - same picture, no beeps, no video signal. Tested those two GPUs on another PC - they work. Also tested another PSU, both seem to work fine on another PC w/o problems.

And so here I am confused. If the MoBo didn't beep at all without RAM then at least I would know 100% the MoBo is dead. But no, MoBo beeps with the correct error tone. But then it should also beep when no GPU is installed, but it doesn't and also doesn't output any video signal with 2x confirmed working GPUs. I am lost at this point.

 

[rgd1101]

what the make and model psu? what gpu did you test with?

 

[Automatron]

what the make and model psu? what gpu did you test with?

Radeon 4850 and 5670. PSU Trust 420W and Coolermaster 500W.