[Power supply flashing on and off]

Hello I recently bought a new Toughpower GF1 750w psu I connected it to my computer with the given cables and when i turned it on it turns on for half a second and then turns off and repeats that cycle. At first i thought it was my mobo that was doing it but i plugged in another psu and it booted just fine. I double checked the cables to make sure one of them wasn’t loose and they were firmly in place. Does anyone know how to fix this?