ATX PSU Switches off Immediately

This is the second PSU that I've had this problem with in the same system, so I'm betting the problem isn't the PSU.

I have a slot 1 mobo with these components hooked up:

CD-ROM
Floppy
HDD

I have a 300W ATX supply for p3/4 systems. Whenever I hook it up and turn it on, it starts to power up for about a second, then it switches off. If I hold the reset button in, everything lights up, but the cpu and fan don't power up, and as soon as I let go, it starts to power up then shuts off right away.

I've tried fiddling with the connectors for the power and LEDs on the mobo to no avail.

Any ideas?

Thanks,
Chris

The mobo got screwed up somehow, so I set the jumper for recovery, pulled the battery for a few minutes, and reset the whole kit n' kaboodle. Booting up A-Ok now!

[edit]
To be specific (mainly for the benefit of googlers and searchers within the forum):

The motherboard is an Intel se440bx-2. There's no momentary switch in the system. There's a BIOS setting for what to do after a power loss. If it's set to "Last State", and there's no momentary switch (have to switch the system off at the PSU), it gets stuck in sleep mode so it turns on, the fan spins for a second, then it shuts off. To fix it, you have to pull the 3-pin jumper on the board for configuration/normal/recovery mode so they're all open (recovery). Turn it on. It will try to read A: for a recovery disk and beep at you. Turn it off. Take the battery out for about fifteen minutes. Put it back in, turn it on, and go into setup. Change the option from "Last State" to "Power On". Set your other settings (like the clock and whatnot) as needed.

AFAIK, this is only a fix for systems with this board and no momentary switch.

Also for the Googlers, there are two other common possibilities that can cause these same symptoms

Scenario 1:

Incorrect or faulty BIOS settings. This is common when a motherboard is moved from one system to another. The solution: reset the motherboard BIOS by moving the jumper on the three pin connector and then moving back. You may also remove the CMOS battery and then replace it. Read the instruction manual for your motherboard to find out which jumper to use.

Scenario 2:

The motherboard is shorting out against the case or another component. To determine if this is the problem, remove the motherboard and set it on a non-conductive surface such as a desk or cardboard box. Install the CPU, heatsink, and memory and connect the power supply and power connectors from the case. (Do not install video cards, sound cards, drives, or other components yet.) This is known as a "bench test". If the computer boots (the BIOS beeps and power lights come on) then unplug the power supply and add components one at a time testing between each one to determine if a components is the culprit. If the system is completely assembled and booting outside the case, then the case is causing the short. Reinstall your motherboard being sure not to make improper contact with the case. You may want to install the motherboard with non-conductive plastic standoffs or remove the Form Factor Panel from the back of the case. I have seen many instances where serial ports were shorting out against the back panel.

hi
i have a similar problem. recently the power suplly had a problem well i was on the computer playing a game and the power just went out. i put a new atx 350 in but it keeps restarting evverytime i try to switch it on. i have a p4c800 a asus motherboard and a p 3.0ghz processor. plz help me out

(~~;(I think your case is not the same.)

Probably shortage of power, remove the peripherals for test.

I read this with interest as I couldn't get my new atx case to power up after switching components. I loosened off the screws which connect the board to the case and hey presto..it powered up!

if you're ever in London I'll buy you a beer

andy