I’ve a hp z400 workstation. I’ve been trying to make it into a budget gaming pc by picking up a seasonic 500w psu and a Radeon HD 7950 I was given for a low price by a friend. The psu I bought was new only opened but even after getting a 24 pin to 24 pin since it’s non proprietary PSU it still won’t boot up. When I click the power button on the pc the fan spins for a millisecond and the psu doesn’t even boot up. Straight after I get 3 loud beeps.