PC not booting....much

[Blues&twos]

Hello. This is my problem....I just have a Mesh PC running win7 home premium 64 bit with an Asus motherboard. This evening it switched off with no warning as if the mains power had been switched off. I removed an old graphics card which had given problems in the past and attempted to boot. Tbe power indicator lit ant the PSU fan came on for about 1 second, then there was a click and everythingg shut down again. Suspecting the PSU had failed I replaced it with one from another Mesh PC- slightly more powerful. This did exactly the same, several times. The PC won't boot.

Any ideas what might be causing it? The PC is about 3 years old.

Thanks in anticipation!

[Saab Dastard]

Any beeps?

SD

[Blues&twos]

No, no beeps, it didn't get that far, literally only a second from me pushing the power button to the indicator lights goinv out and the system powering down. Just tried it again and now about half a second! The fan barely gets a chance to spin before the juice goes off. I am becoming resigned to a trip to the repair emporium....

[Blues&twos]

I will try removing the memory tomorrow and see if the boot process goes any further. I have been informed there were a couple if unexpected bluescreen crashes followed by normal automatic restarts over the last few days.

[Milo Minderbinder]

dead motherboard

However if its the ASUS board I remember, some of them when new had faulty SATA ports. I had to switch a number out onsite for Mesh. Unlikely its the case here, but it may just be worth connecting the drives to the spare SATA ports. Theres a chance one of those bad ports may have fractured and be shorting

[Blues&twos]

Right, update...not looking good for mobo! Took memory cards out, same problem. Unplugged hard drive and DVD drive from SATA sockets on motherboard. Same problem. Unpugged 4 pin 12v cable from motherboard....now fan stays running until mains switched off. At all times, when mains is connected a green LED on motherboard remains lit.

So, to me it looks like the motherboard is indeed embuggerated. PC repair man, here I come.....

Thanks for the questions and suggestions.

[Saab Dastard]

I have seen a case switch be at fault - try removing the jumper block from the switch to the power switch jumper and shorting the jumper manually.

SD

[Blues&twos]

I'll give it a try, but I don't think the switch is faulty as the fan starts and continues to run when tbe switch is pressed....if the motherboard 4 pin plug is unplugged. I'll report back when Ive tried it.

[Saab Dastard]

The switch is responsible for switching off, as well as on... as you say, the system powers off in less than a second...

If you short the jumper block and remove the short, the system will not shut down until you short it again. If the switch is keeping the short in place, it will start and immediately stop.

SD

[Milo Minderbinder]

the only way a switch could be doing this is if its the RESET switch jammed - not the power switch
the machine is powering, its jut not starting up. so the power switch is working

however I'm convinced its a blown board

[Saab Dastard]

Milo, I have to disagree with you here. The reset switch is a separate entity, that does not need to be supported by the case or mobo.

Switching ON requires a transient short of the jumper block, switching OFF also requires a transient short of the same block. If the switch is faulty, it can switch the system on and immediately off.

This is not theory - I have found this particular fault on a Fujitsu system.

SD

[Milo Minderbinder]

see post 6 - the power isn't being switched off
Something is stalling the board, and its most likely incorrect startup voltages - though it could be a short or if the reset switch is jammed "closed"

[Blues&twos]

Hi, have already tried a different PSU, so unless that one is defective too (not impossible) it's probably not the power supplies.

I couldn't short the switch pins on the mobo (combination of dodgy eyesight and poor access), but I did a similar thing and tested the switch operation at the mobo plug end with a mulimeter. The switch and associated wiring/plug are working perfectly. My PC doesn't have a separate reset switch.

I've put it all back together with original PSU, plugged everything in securely and I still have the same fault, so it's looking suspiciously motherboardy. :(

On the positive side, I have learned a little bit about PC troubleshooting I didn't know before....

[Saab Dastard]

literally only a second from me pushing the power button to the indicator lights goinv out and the system powering down. Just tried it again and now about half a second! The fan barely gets a chance to spin before the juice goes off.

The above is what sounded like the switch being a possible fault -

now fan stays running until mains switched off.

But agree that this doesn't.

SD

[Blues&twos]

It's official...motherboard is broken. My friendly, local computer repair man is replacing it if he can get the part. Both of the PSUs were tested and were good, so at least I know I've got a decent spare.

Thanks for the help, everyone!

[green granite]

Interestingly my son's desktop died (he's an electronics service engineer) he changed the psu, despite the volts showing up as correct, for a known good one, still dead, put a new mobo in still dead, puts in new processor still dead, changes the psu for the known good one....it works, so he had a duff psu and mobo he was not amused

[Milo Minderbinder]

doesn't happen so much now, but it used to be a common thing with systems with underpowered PSUs, for the PSU to blow and spike the motherboard at the same time
The worst culprits were Packard Bell (when part of NEC) and Acer. Both tendied to use 145W PSUs for Pentium 4 systems. They were underpowered and heavily stressed - and went bang

It got so bad that for a long time I routinely replaced the PSU every time I replaced a m/b - I didn't want an old PSU taking my new board down and a customer complaining. Problem was both companies sometimes used cases which would only take an m-ATX power unit, not a full sized one - and that limited the options of what could be fitted
Not sure if you can get an m-ATX PSU now

[unclenelli]

What is the ambient temperature?
I've heard of several of the following:

Cracked MOBO overheating and shorting out - but only when hot
CPU overheating
Clogged/dirty heatsink fins
Overloaded PSU
Dirty PSU
Overheating Mem


On the non-temp side:

Flat BIOS Battery
Corrupted BIOS
MBR Virus

[Biggles78]

You mention the machine is about 3 years old. Check the EXACT date and the motherboard on ASUS site. Many of their motherboards have a THREE year warranty and you may be able to get it replaced for free. You will need to do the ASUS RMA and return it to them.

If it is still under warranty and you get it replaced then you can either keep it as a "just in case" or flog it on eBay.