Explain this one if you can

[weird1]

OK- takes a deep breath - please bear with me I'm okish on the technical stuff but no expert for sure!

I have a strange problem with a PC I put together well over a year ago.
All has been fine for many months until about a month ago the PC had a problem booting.
Switched power on at the mains and pressed the old reset button and nada. No fans, nothing.
After a few attempts - switching power off/on at mains it booted again ok. This maybe happened a couple of times. Then the problem then seemed to go away until a couple of weeks ago I noticed a faint electrical burning smell... eek bad sign I thought.
The PC was still running at this stage but I thought I'd best swicth off
Now I can't get the PC to boot (well almost true ... read on).
So ... I ordered a new PSU - ok ok it's only an AOpen 250W PSU but before you falme me that's better than the generic 230W I replaced. I thought this has to fix the problem but no.... still nothing.

Now for the weird part. I thought well maybe the MOBO has burnt out or something - so before I send the PSU back as faulty I'll piggy-back the mobo of another PC's PSU. I've done this 2x now and on both occasions the MOBO powers up - fans whirr etc....
Then - even stranger - I connect back the new 250W supply and 2x now it's done the same thing. First time after I've powered up after using the other PSU it boots up.
But not on any subsequent attempt.

Sorry for the long post but I'm trying to describe in enough detail what's happened.

Has anyone got any ideas what might be wrong here - 'cos it's got me stumped.

 

[weird1]

I think I might have isolated the problem.
When I booted off an alternative PSU I hadn't reconnected the HD's, CDRoms etc.
I have now discovered that I can get the system to power up OK but only if I don't connect the primary HD to the power.
I assume there is some kind of short going on inside the HD.
So looks like I need to get a new HD and have a happy few hours reinstalling.
:beer:

 

[MrChad]

Your power supply may be underpowered. What kind of peripherals do you have connected?

 

[weird1]

Thx for the post.
You're right, I suspect, although I had been running ok previously with 230W supply.
I have 2HDs, CD-Rom , AGP Gfx and PCI sound and network cards (when they are all attached)
It's only a PII-350 (blushes) to play kiddy games and do a bit of internet browsing (the lego website is excellent btw).

I don't believe it. I was sure it was the HD. I repeatedly got it powering up yesterday without the HD attached - and failed with it. But I just tried again now and nothing again.
Ah - I reseated the gfx card (the ONLY device attached) and now it's booting again.
Do you think it might be the MOBO? Maybe the HD thing was a red-herring?

Oh- took the gfx card out to eliminate that problem and now its stopped powering-up again.
There's got to be something more than just the HD at fault I think.
If it's not the MOBO what else? The switch on the case? I tried shorting the jumpers with a screwdriver to test that theory but it wouldn't power-up -would that work anyway?

Btw I've got the MOBO sitting on cardboard out of the case in case there was some kind of short going on in the case.

 

[helpmeout]

Maybe a short on the mobo itself ?