System Malfunction, No (Short lived) power

Hello fellow hardware junkies. I have been interested in computers for many years but have recently stumbled upon a situation where I'm a little unsure what to do next.

Recently my set-up has been acting funny. By this I mean I would press the power button and the system would turn on for 2-8 seconds before shutting off (nothing shows on the monitor). The only thing that happens is the fans spin for this time. If I kept pressing the power switch it would eventually boot. Normally, I would have tried to determine the issue but it was the end of my semester so I just left my machine on so I could continue my work. Also, sometimes when trying to run games the machine would power off suddenly.

Currently I cannot seem to get the machine to power up and remain stable at all. I'm unsure if it's the PSU or my graphics card or the PCIe slots on my mobo. If I do not plug in my graphics card the system will boot which leads me to think its my GPU. I do not know, however, if the GPU could be overloading my PSU and perhaps it is the PSU after-all. My card needs a 12V rail. I don't have any other hardware to test with and I plan on getting a new PSU tomorrow as it's a cheaper check.

I was just wondering if anyone here has had similar problems. I cleaned out my rig today and put it all back together with fresh thermal paste in case it was overheating but I'm still getting the same issue. I don't mind replacing one of the parts but I'm at a loss as to how to narrow down the problem some more. It seems as if the board is shorting because it no longer stays on for 2-8 seconds, the fans spin for about one rotation before the system shuts off again. My PSU light comes on for this time, and remains on if the GPU is not installed. I checked the 12V rails with a multimeter and they are putting out the correct voltage. I've also tried powering the card while not installed into the PCIe slot. This does NOT cause the system to shut off, but I have no display. It's only when I plug it into the PCIe spot that everything fails (I've tried different PCIe slots with similar results). Sounds like the GPU to me but I would like some more opinions.

The system is a bit dated at this point.
Mobo: MSI P6N Diamond
CPU: Intel Q6600
GPU: BFG 640MB Nvidia 8800GTS OC
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  1. Your PSU is of more than adequate size. Quality is another thing.

    Try this:

    The following is an expansion of my troubleshooting tips in the breadboarding link in the "Cannot boot" thread.

    I have tested the following beep patterns on Gigabyte, eVGA, and ECS motherboards. Other BIOS' may be different, but they all use a single short beep for a successful POST.

    Breadboard - that will help isolate any kind of case problem you might have.

    This is a general repair reply. Your system worked, so do not disassemble it. Just disconnect everything from the motherboard, then reassemble and test in stages.

    Breadboard with just motherboard, CPU & HSF, case speaker, and PSU.

    Make sure you plug the CPU power cable in. The system will not boot without it.

    I always breadboard a new build. It takes only a few minutes, and you know you are putting good parts in the case once you are finished.

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

    If no beeps:
    Running fans and drives and motherboard LED's do not necessarily indicate a good PSU. In the absence of a single short beep, they also do not indicate that the system is booting.

    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.

    A way that might be easier is to use the main power plug. Working from the back of the plug where the wires come out, use a bare paperclip to short between the green wire and one of the neighboring black wires. That will do the same thing with an installed PSU. It is also an easy way to bypass a questionable case power switch.

    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, long single beeps, or series of short beeps indicate a problem with the memory. If you get short beeps verify that the memory is in the appropriate motherboard slots.

    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.
    At this point, if the system doesn't work, it's either the video card or an inadequate PSU. Or rarely - the motherboard's PCIe interface.

    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.
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