strange power/boot-up problem

[corybear88]

I installed a new mobo yesterday, and got a really strange problem when I tried to power up the system.

As soon as I plugged the power cord into the back of the machine, it turned itself on (I didn't touch the power switch on the front). It would start the boot-up for about 6 seconds, then completely shut down. Nothing showed on the screen during this time, but the LED on the monitor went from orange to green to show it was getting a signal. Every time I would unplug and replug the power cord it would be the same thing, on for about 6 sec and then complete power down.

I've tried every combination I have (removing stuff down to bare bones, swapping PSUs, etc), and it always does the same thing. I also tried plugging in the system without any of the plugs for power switch, reset switch, etc connected to the mobo and that didn't change anything.

I suspect that somehow I messed up the CPU (overheated?), although maybe there's an outside chance it is the video card. But I don't think the vid card could cause these power issues... Any ideas?

mobo: K7S5A
processor: AMD T-Bird 1.2Ghz
Vid Card: GeForce Mx2 400
Ram: 128 MB SDRAM

[mjc]

Have you tried with the motherboard out of the case?

This seems like a short.

[zfunk]

do you get any post beeps?
it's normal for it to turn on when you plug the power supply into an outlet if the switch on the back is on. also make sure the red switch is set to 115v and not 230. like mjc stated, you could also have a short on the motherboard. i once had a short when i tightened the screws too much on the mounting points for the motherboard. if you don't get any post beeps when you take the memory out and turn it on you may have a bad cpu. i would take the motherboard out of the case and lay it on a piece of cardboard or wood(something that isn't conductive) and just have barebones hooked up (cpu,video,memory,keyboard,monitor) and then turn it on.

[corybear88]

I haven't yet tried taking the mobo out of the machine and running it. I think that may be my last hope.

To answer what questions I remember:

No, I get no post beeps. It is only on for about 6 seconds, and in that time I see fans spinning but hear no beeping.

Yes, I checked that the power supply is at 115V. Just out of curiosity, what would happen if it were at 230v?

I've tried plugging in the cord with switch on and switch off (and switch connector unplugged from mobo). Always the same: it immediately starts when the power cord is plugged in...

zfunk, how did you know you had a short somewhere? What were the symptoms? Did it cause any permanent damage?

Thanks all for the help. It'll probably be a couple of days before I can try the fix but I really appreciate the tips.

Cory

[zfunk]

I didn't know that I had a short. I just had to troubleshoot it to that. If I remember correctly I believe I was getting power to the motherboard(little green light on the board), but it would not do anything else. I don't think the fans were running at all either. I tested the power supply with a paper clip (can't remember what pins to put the ends in though). I took the motherboard out and tried booting it up and it worked fine. I just had the screws to tight or something.

[corybear88]

Thank you! Thank you! It WAS a short, and now the system is up and running. I took the mobo out and ran it barebones out of the case and everything worked. I realized that that there were 8 studs in the case to attach the mobo, but only 6 of them lined up with the holes in the mobo. So I took out the other 2 and there were no more problems.

Thanks again for the troubleshooting suggestion...