If you put a new power supply board into the machine  then i doubt it's going to be the problem , i've heard the Pinscore ones are ok
Also if you have a multi meter just check the voltages coming out of the new power supply board to make sure it has a good 5 volts.

Check all the connector plugs going to the power supply to be sure they are good , especially the large 12 pin square one as it sometimes burns.
Also check that the CN17 connector on the Cpu board is on properly , wouldn't hurt to check all connectors.
You could also have a good visual check of all the switches on the machine for any broken diodes or that the switch isn't shorting against something it shouldn't be.