Motherboard does not boot after hard power off

[hruodr]

OK. So I'd bet you have one connector that's not hooked to anything. Or you can remove a connector to a peripheral device like networking or the graphics card. Black is ground. Measure the voltages on the other pins. You should have something on all or most of them. But you only need to test one connector.

I do not understand. What do you call connector here?
I could remove some peripherals, but not the place where they are connected.
Should I test that peripherals get electricity from their connectors?

Power supply connector pinouts here. This might be a bit tricky to measure however, with the connector plugged in. Perhaps you can try on the other side of the board where the connector pins come through, if you can access the back. What's really needed is a breakout connector cable.

You mean to test that plugged cables of the PSU are really plugged in the motherboard?
i.e. there is really connection?
Why should that have changed with the hard power off?
Why should such a problem prevail after taking other PSU?

look at the screenprint layer on the PCB itself and see if you can identify any test points; there may be test points for 12V, 5V etc.

How to identify them? What should be written there?

OK, here's a useful trick to test the PSU standalone. Check that the PSU is producing the correct output voltages, that's a good first step.

I have done that many times with different PSUs.

I had a M4A88TD or something very close to that model; the BIOS chip was socketed/removable.

In a previous post you see an image of my motherboard. Bellow right, between BIOS Battery and IDE connector you
see a removable chip with 8 pins. Is it that the BIOS Chip?

 

[blackbird9]

OK, I was just going to say follow that video in the first case, to establish whether the psu is working.

 

[hruodr]

I had a BIOSTAR mobo too and booted it to Linux LiveUSB and flashrom'd the ASUS BIOS image to the chip and put that chip in the ASUS board (I broke a pin off the original ASUS chip and took another BIOS chip off a 3rd unrelated board )

I do not understand. You had A, you flashrom'd B and put it in the B board.

 

[hedwards]

It sounds a bit late in the process, but one of the things that I always do first when a system isn't responding to a button, is to disconnect the power and hold the power button for a good 30 seconds. For some reason that seems to dissipate enough of whatever residual power is in the system so that when I plug it back in that the system will respond again to the power. It's usually more of a monitor thing, but I've occasionally had issues with the computer itself not turning on. It's one of the downsides to the more modern power supplies where they turn on and off based on what the system tells it to do.

 

[drhowarddrfine]

What we're trying to do is just establish that the power supply is working with a very fundamental test. By taking the negative lead of the voltmeter, the black one, and touching the black wire of one of the connectors (or the metal of the case but that might not work) and then touching the red lead of your voltmeter to a red wire (likely +5 volts) or yellow (possibly +12 volts) it might indicate your power is OK (though not definitely).