Mobo POSTS but display goes away after few secs.

[lost_in]

Motherboard: ASUS P5KPL-CM
Proc. : Intel E5200 (2.5 GHz)
Memory: 2GB XMS-2
PSU: FSP-360 Watt
GPU: built-in

Problem:
System was running fine. I shut it down properly. I come back home, power on PC, win 7 boots but then display disappears. I tried turn off and on, same thing repeats but now quickly. like for 30 secs. or so after turning on.

I suspected PSU so tested on diff. PSU, same thing happens.
The display just goes away after few seconds, even if I'm in BIOS.
I have isolated the problem to the 12V CPU connector. If you power on system and then remove the 4 pin 12V CPU cable same thing happens.
what's the cause? cause 12V's are still there. I tested it. its like CPU gets 12V supply for few seconds and then it loses the supply?
bad capacitors? even though their is no physical sign.
P.S. Nothbridge and Southbridge aren't heating up or appear warm.

any ideas? do i need a new mobo?

.

 

[ko888]

Did you try booting up Windows 7 in Safe Mode?

If the problem doesn't occur in Safe Mode then I would suspect a chipset/graphics device driver problem (i.e. when the device driver gets loaded the problem is triggered).

If the problem still occurs in Safe Mode then I would suspect hardware (i.e. Intel GMA 3100 IGP on the Intel G31 chipset) or even memory modules.

You can download and run Memtest86+ to determine if there are any problems with the DIMMs.

 

[lost_in]

^ I have nothing attached to the mobo. no HDD, PCI card or GFX card. Porblem began with 4850 installed so i removed it.
It should at least stay in BIOS..when i enter in BIOS, it at most gives display for like 40 seconds the poof.. no display

 

[jsc]

I have tested the following beeps patterns on Gigabyte, eVGA, and ECS motherboards. Other BIOS' may be different.

Breadboard - that will help isolate any kind of case problem you might have.
http://www.tomshardware.com/forum/262730-31-breadboarding

Breadboard with just motherboard, CPU & HSF, case speaker, and PSU. You do have a case speaker installed, right? If not, you really, really need one. If your case or motherboard didn't come with a system speaker, you can buy one here:
http://www.cwc-group.com/casp.html

You can turn on the PC by momentarily shorting the two pins that the case power switch goes to. You should hear a series of long, single beeps indicating memory problems. Silence indicates a problem with (in most likely order) the PSU, motherboard, or CPU.

Motherboard LED's mean very little. When on, all they are telling you is that the computer os plugged into a live power socket and the PSU is switched.

Remember, at this time, you do not have a graphics card installed so the load on your PSU will be reduced.

If no beeps:
At this point, you can sort of check the PSU. Try to borrow a known good PSU of around 550 - 600 watts. That will power just about any system with a single GPU. If you cannot do that, use a DMM to measure the voltages. Measure between the colored wires and either chassis ground or the black wires. Yellow wires should be 12 volts. Red wires: +5 volts, orange wires: +3.3 volts, blue wire : -12 volts, violet wire: 5 volts always on. Tolerances are +/- 5% except for the -12 volts which is +/- 10%.

The gray wire is really important. It should go from 0 to +5 volts when you turn the PSU on with the case switch. CPU needs this signal to boot.

You can turn on the PSU by completely disconnecting the PSU and using a paperclip or jumper wire to short the green wire to one of the neighboring black wires.
http://www.youtube.com/watch?v=5FWXgQSokF4&feature=youtube_gdata

This checks the PSU under no load conditions, so it is not completely reliable. But if it can not pass this, it is dead. Then repeat the checks with the PSU plugged into the computer to put a load on the PSU.

If the system beeps:
If it looks like the PSU is good, install a memory stick. Boot. Beep pattern should change to one long and several short beeps indicating a missing graphics card. Silence or long single beeps indicate a problem with the memory.

Insert the video card and connect any necessary PCIe power connectors. Boot. At this point, the system should POST successfully (a single short beep). Notice that you do not need keyboard, mouse, monitor, or drives to successfully POST.

Now start connecting the rest of the devices starting with the monitor, then keyboard and mouse, then the rest of the devices, testing after each step. It's possible that you can pass the POST with a defective video card. The POST routines can only check the video interface. It cannot check the internal parts of the video card.