I recently had a motherboard fry on me a ECS P4M800PR0-M. So I bought a replacement a ECS RS400-A. I installed the RS400-A and noticed that my computer would boot for about two seconds then turn off. It didn't even get to post but I could hear the machine booting up (dvd-rom, hard disks) ect. I unpluged every thing and only left the power supply and the motherboard and it still would only turn on for about a few seconds before shutting off. Again no post. I went out and got another power supply and installed it thinking my older supply was fried too. But after I installed the newer one, it does the same thing. I noticed that if I don't plug in the 12v connector into the motherboard the computer will turn on and stay on but will not post or boot. If I do plug it in my comp will boot and turn off before the post screen. I have been racking my brain trying to figure this out. Anyone have any clue or solutions???

System:
RS400-A
Pentium 4 3.6
2 512ghz DDR2
1 DVD-rom
1 DVD-RW DL
2 IDE Hard Drives
1 SATA Hard Drive

1 AGP Ati X1300 512 mb
Gigabit Network Adpt.
Thanks.

ok reset the BIOS

"how?"
simply... just thake the Li-ion battery(the big clock battery) out of the motherboard and wait at least 10 minutes and put it back in and walla... it might work!!!!! =]

Check the cpu heatsink fan and be sure it's plugged into the correct header. Also, check to be sure the heatsink is making good contact with the cpu. You might also have an extra standoff shorting the board.

Tried reseting the bios and checking motherboard connections its still not booting.

Your board may not be able to recognize your cpu. Some boards behave that way when they cannot identify certain cpu's

try a different memory as well just in case..

i once had to replace my memory after my comp would turn on but nothing would show on the monitor.