Hello, my problem began when I decided to build my first PC a little over a year ago (Dec. 2009):
ASUS P7P55D EVO Motherboard
Intel Core i5 750 CPU
Nvidia GeForce GTX 275 Video card
2 x 2GB Team Group Xtreem PC3-12800 DDR3 1600MHz 1.65v RAM
1 TB Western Digital Caviar Black HD
Cooler Master Silent Pro 1000w PSU
Cooler Master HAF 922 Case
The initial boot up was a success, and I proceeded to install Windows 7 64-bit and download all the updates, etc, without any problems. That same night I attempted to shut the PC off and turn it back on, however it failed to boot. Instead, the fans (including CPU fan) spun for a split second and then stopped, and that was as far as it got. I also noticed the CPU and RAM LED lights coming on during this brief time. The LED power light on the motherboard stayed illuminated as long as the PSU was turned on. If I turned the PSU or powerbar off and back on then I could press the power button and get the same brief fan spin up. I continued to try to power on my PC until eventually it actually booted up successfully a day or two later, without me modifying anything. However, after I left the PC unattended for a few hours I came back to see that it had shut itself off and it was back to doing the brief fan spin up when I tried to turn it on. I then tried deconstructing the PC one component at a time, and tried to power it up after each removal of a different component. It still exhibited the same brief fan spin up even when the mobo was out of the case with only the CPU and the PSU connected to it. I figured the problem had to be either the motherboard or PSU, so I tested the PSU with a multimeter and every voltage reading was correct. Therefore I decided it had to be the motherboard, and so I got a replacement.
The second motherboard seemed to work fine. This time my PC worked for about a year without any problems. About two months ago however, I came into my room to find that my PC had shut itself off and there was an electrical burning smell in my room. I found a charred spot on the mobo in the bottom left corner above the 1394a port. The computer was back to doing the same brief fan spin when I tried to turn it on. I RMA'd the mobo and got a third one.
Finally, I put my PC together with the third motherboard. It booted up just fine the time... Once again however, like my first mobo, the PC had shut itself off after being unattended for a couple hours. Now I am in the same situation with the fans spinning briefly whenever I try to turn it on.
After three motherboards not working, I really have no idea what to do anymore. I'm starting to think that it may be something else that is the problem. Is it possible that the PSU could be the problem even though the mobo power LED comes on when I turn the PSU on, and that the multimeter shows correct voltages??
Is it possible that it could be anything other then the PSU or mobo? I figured if it was the CPU, RAM or video card that was the problem that the PC would atleast partially boot up then make some beeping noises and the LED's would come on. But I could be wrong.
Or there is the chance that I did actually get 3 faulty mobo's, if that's the case I guess I should think about buying a new model...
Is it possible that the PSU could be the problem even though the mobo power LED comes on when I turn the PSU on, and that the multimeter shows correct voltages??
It's possible that when the PSU is put under stress something bad is happening. But that is a great PSU.
It could be something bad happened with the AC power. To damage the PSU or even create a problem that ate the motherboard.
Have you talked to Asus? I don't really have any idea what the problem actually is but it could be one of those compound A+B problems that are the hardest to solve. A works, B works, but A+B together can have problems.
Update: So far with my third motherboard I have disassembled the PC 1 piece at a time and tried powering it on after I removed each piece, but it never booted. After leaving the motherboard with the CPU attached out of the case for a day, I hooked it back to just the PSU and tried powering it on. This time it worked. Then I shut it off, turned the PSU off and back on, then tried powering up the motherboard+CPU again and it failed.
So basically whats happening is if I leave the PC turned off for a certain amount of time (about a day), it will start up. But then it may either shut itself off after 2-3 hours or if I shut it off manually and then try to start it up again it will just do the brief fan spin up and not boot. What makes this even more confusing though is that my second motherboard worked for a year without any of these problems.
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.
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.