Mobo turns on only with PSU switch...

< What the title says > Why does this happen? I've seen it twice before on customer's computers, but now I'm putting a cheapo one together and it's doing it.

**What I have hooked up: mobo, cpu, ram, video, psu (no case)**

Every single time here's what happens:
I turn on the PSU (via the power switch behind it) and the whole computer turns on, posts and all. Then, I turn off PSU, wait for LEDs to turn off, and when I turn PSU back on the system turns on again. If I don't wait for the LED to turn off, then it won't give me this problem, but every cold boot with the power switch and the computer fires up.

So far, the front panel power switch (with my screwdriver) doesn't work at all.

WTF?

There is a setting in BIOS that dictates how the PC acts after loosing power. Yours is probably set to "Power On". I prefer "Last State" - so if the PC was off when the PS is turned off, it stays off if you turn the PS back on (until you hit the power button). If the PC was ON when the PS is turned off, it will turn back on as soon as the PS is turned on (like a power outage, etc).

That's my guess, and I'm sticking to it

I would agree the bios seems to be the issue. That puzzled me as well when building Navi; she would randomly boot on PSU power-on and case power button would not work. Power On seems to be the default power setting for most if not all bioses; I've seen that before on relatives' rigs.

ACPCI could be messed also.

I had that problem with a gigabyte. I had an LED wired to the PWR ON instead.

MadSkillzMan said:

I had that problem with a gigabyte. I had an LED wired to the PWR ON instead.

Click to expand...

It could be a similar short somewhere.

I don't have anything hooked up to the front panel jumpers. I'm just using the screwdriver method to turn the PC on.

Are you sure nothing on the back of the board is shorting? Did you check power-on bios settings as suggested?

is it possible that the mobo could detect theres no jumpers and as a result be always on?

MadSkillzMan said:

is it possible that the mobo could detect theres no jumpers and as a result be always on?

Click to expand...

No, because even when you install a switch it's not making any kind of termination until you toggle the switch.

After testing different BIOS settings I'd test the motheboard and vital hardware outside of the case to make sure the motherobard isn't shorting on something.