After being shutdown, why won't my computer start without leaving the power unplugged first?

Question

For the past few months, whenever I shut my computer down fully and leave it off for more than a few minutes, it won't start back up without an elaborate ritual. This is an ordinary shutdown, so the power cable is still connected, and the power supply is still switched on.

When it's in this non-starting state, the power button does nothing; no lights, no fans. However, if I then unplug the machine and wait 5+ minutes, it'll start fine on the first try. The system is otherwise fine.

Worryingly, this occasionally but not always triggers the BIOS recovery feature on my Gigabyte motherboard that detects a corrupted BIOS and reflashes it automatically. I'm worried that some part is headed for a more dramatic failure.

Any thoughts on which component could be causing this symptom?

Solution 1

It was a failing power supply.

This latest time, it just wouldn't start back up. I tried replacing the CMOS battery per davidgo's answer, but that didn't work either. I found a guide for manually testing a PSU, and with it disconnected from everything but the wall, switched it on with pins 15 and 16 jumped. These are supposed to signal the PSU that it's on and should start spinning its fans, but nothing happened.

I did buy it in January 2006, so it certainly doesn't owe me anything!

Solution 2

I don't think this necessarily portends a dramatic failure - you will most likely find the culprit is a backup battery on the motherboard which needs replacing (typically a button battery like a CR2032 which is quite cheap, and which you should be able to pick up at your local supermarket or hardware store).

An alternative possibility is an issue with the power supply in the computer. Generally these can be replaced for very roughly US$100 (assuming it's not a high power computer like a dedicated gaming PC). I'd try replacing the battery, and if that fails go to a PC store and replace the power supply.

Comments

[Thalys]

I'd try the PSU. I've seen that happen with faulty PSUs

[Blaine]

could be a failing cmos too

[Thalys]

you could get a VERY nice PSU for that much.

[davidgo]

Wish we got computer bits for what you do then. A typical 500 watt 80+PSU costs around $100 in New Zealand (from the biggest PC retailer), so not an entry level one, but not exactly high spec.

[Thalys]

The coolermaster I have in my shared desktop is ~80, and the seasonic m12 I have on my gaming rig is about 40 dollars more. I can get a cheap crappy PSU for about 20 dollars. So yeah, I guess its a lot cheaper here.

[Adam]

Hmm, I just tried swapping in a fresh battery, and no luck. Unlike previous times where this problem has come up, leaving it unplugged has not resolved things, so I might have to go ahead with a new PSU.

[Ramhound]

Almost a decade damn good PSU

[Adam]

Indeed. I'll be buying another Antec for sure.

[Ramhound]

Can you better explain how this is connected to the author's problem?