You'll need a Volt Meter and research "power supply green wire test" to see if the power supplies are coming up.
There are too many reasons for this to fail. For example you may need some other ATX12V power lead that is common but you omitted so much detail that all I can do is note these items.
I have a 24 pin motherboard and the pc would shut off after 30 mins with the original 300 watt power supply. I went to put a 20 pin power supply in place that was 250 watts and it powered up but nothing shows on the monitor except the screen lights up black. It also would not power off so I had to shut off the surge protector. I went to put the original 300 watt psu in and it still does the same thing. Could I have shorted something out or do I just need a new power supply?