PC wont start until...

[teresa]

I'm having serious issues with a Dell Dimension 8400 desktop PC. It's a friend of mine's PC.
Pentium 4, 1Gb RAM, 145GB HDD, Radeon X300 video card, Creative Soundblaster sound card

A few days ago, 30 seconds after turning PC on, the computer shut down and wouldn't restart.
The power button would flash amber in colour and only the fan on the PSU would work.
There also was a small green light on motherboard that would light up but that was it - no life anywhere else in system.

I proceeded to unplug hard drive, take out RAM and pulled out all PCI cards then put everything back and turned PC on. This time the PC turned on and stayed on all day.

I returned the PC back to my friend who after a day or so began having problems again. The PC would shut itself off after being on for 30 seconds or so buut she could turn it back on.

We contacted Dell who (whether they may have misunderstood me - I'm not sure) seemed to think it was a software issue. So I proceeded to do a Dell Diagnostic which did not detect any errors and then I proceeded with doing a recovery which did pick up on errors and corrected them.

The next day my friend was using her PC, it froze completely and she was unable to turn it off. She ended up switching it off at the powerpoint but then it wouldn't turn on - the initial problem above had occurred. I had to unplug and pull out cables and cards and put them back in for PC to start but this time PC would not detect DVD drive which after a couple of attempts have sorted that out.

The PC has now been running for 5 hours without incidence at my place. I have opened up multiple programs while running Nortons antivirus scan to put the PC to the test & there has been no problem.

Can you help? Please...

[glc]

If the 4 LED lights on the back (A, B, C, D) are ever NOT all 4 green, note which is what and look them up in the online service manual for a clue to the problem.

If all diagnostics passed, I'd suspect either overheating or a defective power supply.

[teresa]

Cheers. All 4 lights are green. After the first time PC wouldn't start and when I did get it started, the lights had indicated some type of failure - it didn't really specify what though.
I'm not sure if overheating is issue but I won't rule it out yet.
Is there any further way of testing to see if PSU is faulty?

[glc]

Not without some way of dynamically monitoring the voltages - or by substituting a known good unit. Same for overheating - you have to be able to dynamically monitor the CPU temperature.

[teresa]

PC ran well all night. All that was plugged into PC was monitor, keyboard & mouse. I then decided to put PC to the test & connected a USB network adaptor and speakers. The computer has now died and will not start at all. The PSU fan runs, there's a small green light on motherboard & the power light stays a steady amber/yellow.

Does it sound like the PSU?

The PSU in Dell PC has a 24 pin coonnector for mo'bo. I do have another PSU but it only has 18 pin connector for mo'bo - is this a problem?

So much for Dell Technician, thinking it was software issue.

Please help....

[jfk]

My guess is the PSU bought the farm. Yes, you need a proper ATX 2.0 designed PSU with a 24 pin connector for the mobo.

[teresa]

Thankyou.

What I discovered is that the 4 pin connector from PSU to motherboard has shorted out the motherboard. Connector looks burnt. Bugger! Which means motherboard to be replaced & probably PSU too.