When 12v 4 pin connected comp shuts down

[Dryst999]

I have a pentium 4, 3.2 ghz w/ ht on an msi board.

My problem is when I try to turn it on, it will turn on for a second
then turn right off, and there is usually a sound (hard to explain.
Anywho, in my diagnosing efforts, I've come to the conclusion that the
12v 4 pin connectior on the motherboard (right next to the processor
is what is causing the issue. When I unplug it, the computer will start
fine, but I will get nothing on the monitor (with my gfx card, and with
onboard.)


MY QUESTION IS, COULD THIS BE CAUSED BY A BAD MOTHERBOARD? OR HOW CAN
GET MY COMPUTER RUNNING AGAIN

thanks

cliffs: pc wont stay on, stays on (but no monitor) when 12v 4 pi
connector removed from mobo

 

[SNGX1275]

This is going on the theory that perhaps one of your 12V rails on your PSU is toast. Proceed at your own risk. I'd rather you wait for someone else to reply with an ide before trying this, since its sort of drastic.

Since you've already wired a switch, I'm going to assume you feel somewhat comfortable with the wiring. I'd determine which pins are what on the 4 pin plug, and then cut off one of your molex connectors (that will have 1 12V and 2 grounds and 1 5V), maybe cut 2 if you need 2 12V I'm not sure how those are wired up. Anyway, make your own 4 pin 12V connector and use that.

Plugging it in and getting a spark then a shutdown probably isn't real safe to do, and you could have broke your motherboard from doing that...

 

[Dryst999]

Yeh well i'm trying to determine if my motherboard is screwed to begin with. It just makes no sense to me that everything runs fine until I plug in the 12v 4 connector. To my understanding that connector is only used to help power the motherboard and the fans on the computer... why would my monitor not come on if I don't plug it in?

 

[mailpup]

Because if the motherboard isn't working regardless of the reason, you aren't going to get a display on the monitor. The 12V 2x2 connector is for the CPU and not an optional or ancillary power connector. That spark you created everytime you plugged it in while it was running could have killed the motherboard in and of itself.

Do you have another power supply that you can substitute for test purposes?

 

[Dryst999]

Ok edited my post... just to clarify that wasn't my original post. I'm having the EXACT same problem and during my research on the net I saw that post with no answers so I just cut and pasted since he explained it so well lol. I never plugged my PSU into the motherboard while it was on i'm not that dumb.


I took my MB out of the case and put it on cardboard to make sure it wasn't being barred and it still had the same problem. Would turn on fine without the 12v plugged in but as soon as I plugged in the 12v it would go completely dead, the fan would turn on for half a second then nothing.