Try to clear the CMOS before attempting anything else.

Disconnect the PSU, take out the coin cell battery, press the Power button on the case to discharge any leftover energy and then set the clear CMOS jumper to the relevant position. Wait about a minute then set the jumper back, put the battery back in, reconnect the PSU and then try booting the system up again.

Joseph_Joestar wrote on 2022-03-09, 20:17:

Try to clear the CMOS before attempting anything else.

Disconnect the PSU, take out the coin cell battery, press the Power button on the case to discharge any leftover energy and then set the clear CMOS jumper to the relevant position. Wait about a minute then set the jumper back, put the battery back in, reconnect the PSU and then try booting the system up again.

Thanks for the suggestion, but already been there and done that; no effect.

A7v and A7V 133 motherboards are both notorious for suddenly stopping POSTing - do a Google search and you'll find many examples of people asking for help with this issue. Sometimes it takes strange things to get them to come back to life. I'd try a 100 MHz FSB Athlon or Duron if you have one, preferably with a PCI video card.

Back in 2006 I was given one of these and I used it to build a system I gave to a relative. At some point (after working normally for a while) it didn't want to POST and I remember nearly giving up on it out of frustration before I finally tried something ( I can't remember what) and it began working normally again.

dormcat wrote on 2022-03-09, 20:05:

The on-board power LED is lit, but cooling fans and HDD motor wouldn't budge.

That sounds odd, don't hard drives spin up as soon as 12V is applied? Are the cooling fans on motherboard headers, or plugged directly to the PSU? Can you measure what the 12V line is on a molex connector?

Similar symptoms, but unlikely the same cause:
P3B-F stopped working...need help
My ASUS P2B motherboard died suddenly

snufkin wrote on 2022-03-09, 21:28:

That sounds odd, don't hard drives spin up as soon as 12V is applied? Are the cooling fans on motherboard headers, or plugged directly to the PSU? Can you measure what the 12V line is on a molex connector?

A PSU doesn't just output 12V when plugged in or switched on by its own; it requires a shorted signal from MB, specifically, the green PS_ON# wire shorted with a ground (black) wire. I've never shorted the green PS_ON# wire with a ground wire directly before so I'm a bit hesitant to do so; I connected the PSU to another MB and it worked fine so the problem should be on the A7V133-C.

Cooling fans were on MB headers so I connected another working one to a Molex; not spinning. Either there's something wrong between the power switch pins and the PS_ON# wire, or the problem is even deeper and bigger. 🙄

dormcat wrote on 2022-03-11, 10:00:

snufkin wrote on 2022-03-09, 21:28:

That sounds odd, don't hard drives spin up as soon as 12V is applied? Are the cooling fans on motherboard headers, or plugged directly to the PSU? Can you measure what the 12V line is on a molex connector?

A PSU doesn't just output 12V when plugged in or switched on by its own; it requires a shorted signal from MB, specifically, the green PS_ON# wire shorted with a ground (black) wire. I've never shorted the green PS_ON# wire with a ground wire directly before so I'm a bit hesitant to do so; I connected the PSU to another MB and it worked fine so the problem should be on the A7V133-C.

Cooling fans were on MB headers so I connected another working one to a Molex; not spinning. Either there's something wrong between the power switch pins and the PS_ON# wire, or the problem is even deeper and bigger. 🙄

Ah, I was assuming that the on board power LED would be powered either directly from +5V or from a power good type signal, so would only light up if the PSU was fully on, which would be odd if the HDD didn't then spin up. If the PSU isn't starting up, but the LED is on, then it must be powered from +5SB.