Bad Motherboard?

[studiot]

I still don't understand what you are saying.

If you had the psu connected to a psu tester, how did the computer manage to start?

The original symptom you describe is consistent with a fault being detected very early on in POST. The keyboard check comes almost at the beginning in Dell BIOS.

So the pc starts, but quickly finds a fault (eg a shorted usb or keyboard etc) and shuts down again.

Incidentally although the 8400 is an old model it is new enough that the psu has a conventional power wiring. Olders Dells ( and Compaqs) may not.

[drewm]

Thanks for you help, all. I guess I am not very good at explaining what is going on in this situation. My apologies. I'll get it. I just need to put on my big-boy pants and see what I can do. I have a POST diag card on order, so that should help me some. Thank you for all your comments. Again, I'm sorry.

[Skyhooker]

I'm still not clear on the symptoms. Are you saying that the computer doesn't run after you connect everything and press the start button, or is the problem you're describing only that brief spin-up of the power supply fan and the LEDs that come on at that time? If only the latter, and the computer actually runs normally when you then press the start button, I believe that's just the normal self-test that the Dell power supplies themselves run when connected to power (at least the older ones).

Sorry, but I just couldn't find where you said it simply wouldn't run at all (apologies if you did - it's early and the coffee's still kicking in ).

[gazza]

Hey DrewM,

I would try turning off your computer disconnecting the power cord and taking the cmos battery out of the motherboard for 10 minutes then replace it and restart the computer.

[PcTek9]

1.) does windows ever come on the screen ?


Do keep in mind that some post cards can help you differentiate between a dead cpu and a dead motherboard.
Some post cards have like 8 LED's in adittion to the numeric led's, and the 8 LED's represent among other things,
if it is the cpu or the motherboard that is dead. (something that can be very hard to tell if you dont have a known working cpu for every model of cpu laying around...)

[atlanticjim]

Originally Posted by studiot

So the pc starts, but quickly finds a fault (eg a shorted usb or keyboard etc) and shuts down again.

1+ I have had this problem now twice on a Dell Mobo. One was a trashed USB next to the switches (plugged into the mobo) and the other was one of the USB on the Mobo back panel itself. In the end an easy fix (and in my diag list).