old computer power supply

Hey all,
I got a old computer and I decided to get some components from it. The power supply was one of them. I saw that if we connect the green wire with any of the blacks, I could make the PSU start, but that isn't hapenning. But whenever connected to the motherboard it works fine. The model is PDP-116P from COMPAQ with an output of 24 pins. Can someone help me to get it working? I already googled the pinout but nothing that I found worked. I also tried connecting white and grey wires.

Thanks in advance

As far as I know, every ATX power supply will power up if you connect the green wire to ground. There is only one green wire but there are several grounds. Make sure it is a ground wire you are connecting it to.

I opened the box and all black wires came from a "zone" that says GND, also, when connected to the motherboard, measuring the voltage all black wires are ground. I tried the green wire with all the black, it never worked. I also saw somewhere that COMPAQ PSU's have a completely different pinout from the "standard", as seen here: Compaq 24 pin power connector pinout

Hi again,
I made some search and I found this:
https://www.experts-exchange.com/Hardware/Components/A_3940-Use-a-Compaq-200-Watt-Power-Supply-PSU-as-a-second-power-source.html.
But the PSU only turns on for a few seconds, any idea to fix this?

Compaq... Like HP, great stuff but always have to ad their own little proprietary bit or something to make it incompatible (or inCompaqable) with other industry standard designs or interfaces.

Maybe they require a minimum load (for regulator tho that IMO is doubtful) or have current sensing circuitry...

For the $5 or $10 it would cost, I'd get another brand PSU if you can't find a discarded PC by the road - that if the fun or your patience runs out, or you have a use for it.

Probably is the best thing to do, to buy other PSU. By the way, what should I do to this one?

Turn it off.