Help! Parent's computer won't boot

[stroberaver]

Hi,

I've got my parent's computer in my custody for repairs. It won't boot up - everything switches on and hums for a couple of seconds, then it just shuts down again. It's a basic machine - one dvd drive, one hard disk, onboard video. Not really much to go wrong, or so I thought!

At first I thought it was the PSU, as I noticed the rear fan on the Antec SmartPower unit (SP450-P) wasn't turning. However I've swapped in a spare, old Chieftec 360W unit, and it still won't boot. The Chieftec PSU only has a 20-pin ATX connector instead of the 24 on the motherboard, but the mobo manual says it should still run fine on 20 pins if it can supply more than 15A on 12+V (which it can).

I've swapped the hard drive for a known working one, disconnected the dvd drive, floppy, pretty much everything I can. Still won't boot - just hums into life for a couple of seconds, everything looking normal, the CPU fan is working, then it all shuts down.

Motherboard: Asus m2npv-mx
CPU: A lowish spec Athlon (can't remember the spec, was a while ago I built the system)

Problem is I've got nothing to diagnose it with - no boot/POST screen, no BIOS beeps, it just turns itself off.

Can anyone suggest anything to try next?

Many thanks in advance.

[Stephen C]

Could try reseating the CPU and adding some new thermal compound, sounds to me like something's overheating or not getting enough power. Probably the latter if you've had it apart for a while then tried it again.

[MaddAussie]

Id check for a short somewhere, or a sticky power switch

[stroberaver]

Cheers, all the generic self-help guides I can find that refer to a computer immediately turning itself off also seem to suggest a short or electrical fault somewhere. Guess I'll be dismantling the front bezel of the case to check and clean the switches and/or removing the motherboard - gonna take a bit longer than I originally thought!

Curious thing is, the computer just suddenly wouldn't turn on one day, so it's hard to see how it would be overheating or developing electrical faults. My only fear is that the failed fan on the original PSU (even though it was a push/pull dual fan arrangement, and the other fan was still working) has affected the PSU which in turn has affected the mobo or cpu. As I've swapped every single other component except these two, it's either one of them or an electrical fault.

[killie99]

any sign of bulging caps on the motherboard?

[stroberaver]

I checked the motherboard for any signs of anything blackened, burnt or blown (there was nothing).

By bulging, do you really mean looking swollen and enlarged?

Can't say I noticed any caps looking like that, but will check more closely when I get home from work. Thanks for the suggestion.

[stroberaver]

Hmm, nothing visibly wrong with any of the caps.

Tonight I've had the motherboard unseated and out the case, checked for anything behind it or anything dodgy looking on the rear, put it back in, and still the same. That even includes booting it up with nothing attached. I've powered it up when out of the case, resting on some cardboard, but still the same - no POST, shuts down within 2 seconds.

I'm stumped. Anything else I can try? I'm wondering whether to consider getting a cheap AM2 cpu off ebay to try swapping in. If it still does it, I know the mobo is goosed.

[Stephen C]

Other than resetting the CMOS which I'm sure you've done, re-seat the CPU. Looks like you've tried everything else.

[killie99]

bulging caps ....

http://en.wikipedia.org/wiki/Capacitor_plague

[stroberaver]

Other than resetting the CMOS which I'm sure you've done, re-seat the CPU. Looks like you've tried everything else.

Yep, already done the CMOS, but have just done both the things you mentioned again, right now. Still no change.

bulging caps ....

http://en.wikipedia.org/wiki/Capacitor_plague

Ah, thanks for that, wasn't aware of that stuff. I can definitely say that I don't have any bulging caps with electrolyte leaking anywhere. One of them is at a bit of an angle, but could've been like that from new - nothing else suspect about it.

Seems like it's just plain cream crackered. My parents aren't too chuffed about it, and neither am I tbh - I thought this computer should easily last more than four years!