I just bought a new 650 watt PSU and installed it in my PC (it was home built, the PSU was going out on it). I flicked on the power switch in the back, saw the blue LEDs on my motherboard turn on, then tried to turn on the computer...
It started to turn on, but turned off after a second and the LEDs on my motherboard went off. Now it won't do anything when I try to turn the computer on.
My first thought was that the PSU spiked and killed my mobo. I'm not sure, though-- has anyone else had this problem?
Both were connected when I closed the case, although the aux cable (8 pin) was a little loose. It's on my list of things to check when I can drag myself back in there to look at it (back and neck killing me right now).
I very quickly switched out the power supplies (didn't even hook the old one up to anything but the mobo) and my motherboard seems to be intact judging by the LEDs (which came back on with the old PSU). So I guess I'm either looking at a dead PSU or possibly user error.
Strange thing, though-- my motherboard has an eight pin aux connection but the old PSU connects to it with just four pins.(A while back I took it to the shop to have the PSU replaced because I didn't have time to do it myself, so I know nothing about this PSU) The new PSU has eight pins.
Not sure if that helps any, but thought it deserved mentioning.
If your mobo has an 8-pin connector, you can use either a 4-pin or 8-pin connection with no real difference in performance. If you are OCing your system you should use 8-pins, otherwise, it really doesn't matter in most cases.
Will the system boot with the old PSU?
Also, with the new PSU, you can try this. With only the PSU attached to the mobo and the GPU (if required) and NO other devices, see if the system will boot to the point where you can enter the BIOS.
That would indicate a short or bad power connector.
What make and model of PSU is your new one and is it a modular PSU?