Power Problems

[python023]

I have a system that is behaving quite erractically: it powers on and off at will. As soon as i plug in the power cable/flip the switch on the PSU it will start, and randomly turn on and off until i pull the plug. I have swapped in and out RAM and Gfx card to no avail. It outputs nothing to the screen, just powers on and off. It sounds out no beep codes, but all the fans spin up. The motherboard seems slightly loose and i may have to resort to reinstalling each piece of hardware.
System Specs:
WinXP Pro
Intel P4
ASRock P4i45E
512mb PC3200RAM
ATi Radeon 9200

Any other ideas as to solving this problem?
thanks

 

[FlyingPenguin]

My first thought would be that the front power switch is shorted out. If it stays pressed it will power off the computer every 5 seconds and then restart.

Try disconnecting the power switch from the mobo and see if it still happens. If not, short out the pins on the mobo header for the power switch with a screw driver to turn the mobo on and see if it stays on.

 

[python023]

I swapped out powersupply - a working PSU gave me the same problem, whereas the "bad" PSU worked in another system. The front power switch is not the problem because the system still turns on and off at random even when the power switch is disconnected from the mobo. I removed everything and reinstalled all the hardware, and still had the same problems. The motherboard does not have any physical problems - no bad caps or breaks or anything like that. Any other ideas?
thanks

 

[montag451]

Can you also take the reset sw wires off the header

 

[python023]

These quotes came from another forum:

Quote:
did you try the motherboard outside the case on a nonconductive surface?


Tried that - same problem.

Quote:
I had a similar problem in the past caused by a bad connection between the cpu and heatsink - try removing the heatsink and clean off the cpu and bottom of heatsink with rubbing alcohol - make sure u still have a nice flat surface ont he bottom of the heatsink - put a spot of thermal grease on there - spread it thin and remount the heatsink/fan - try it in a diff position - could turn the heatsink 180 degrees - see if mounting is easier - if it's harder to mount that way, turn it back the other way - a bad connection between the CPU and heatsink will cause the machine to turn on and then shut off immediatly. Try it.


Did that - same problem.

I cant see any physical damage to the board, so what could be causing this?
thanks