I upgraded my PSU on my HP H8-1234 with a Corsair TX650 V2. When I press the power button, the fans turn On for a second then everything shuts down. This happens as I fully press the Power button down then again as I let go of the button. Bottom line is that my desktop does not Power On when using the Corsait TX650. This is the third unit of the same model that I have tried and all did the same thing. I then used a Thermaltake 600 PSU and it worked just fine. I don't think its the TX650 that has a problem but it seems that there is an incompatibility between my H8-1234 and the TX650. Any advise? I really prefer to use the TX650 over the Thermaltake.
I am having a similar problem. I have the same HP computer and when trying to upgrade my PSU it is doing the same thing as the OP's problem. Flickers for a half second and off. I have tried both the Thermaltake Smart Series 750W and 850W. Both do the same thing. Any answers?
Apparently I ended up returning the Corsair PSU and settled for a Thermaltake TR2 600W PSU which worked just fine without any problems. It seems that the Power switch of the HP H8-1234 has a compatibility issue with PSU Power switch.
Best Buy geek squad figured out what the problem was for my particular unit. All of the thermaltake's were outputting 12.1 V when the motherboard was requiring 12.2 V. That small difference created all the chaos.