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Computer turns itself off after a split second of turning on?

Last response: in Components
August 21, 2010 2:18:12 AM

Hello, I have a problem with booting up my computer. Everything was running fine until I left on the computer overnight and waking up to see that it turned off by itself. Everytime I turn it on, I find the back fan LED and moving for one second and then off. I suspect it was the power supply and I replaced it with a new one but it still has the problem. I also took out the video card, took out RAM and removed the motherboard studs but the thing doesn't turn on. I'm just so frustrated that it happened at a bad time.

There is no smoke odor coming from the old PSU. And the motherboard looks fine with all the capacitors looking functional. Also there's no heat activity for the motherboard or CPU to shut itself down. Are there any other signs to tell if it is a CPU or motherboard problem? Thanks in advance.


mobo: MSI K9AG NEO2 Digital ver 1.0

RAM: OCZ PC2-6400 ATI CrossFire 2 GB set

Graphics Card: Sapphire ATI Radeon Crossfire 3870 Toxic HD 512MB 256-bit GDDR4 PCI Express

PSU: Raidmax RX-630Z 630W ATX

Sound Card: ASUS D2X Xonar Dolby Digital

HDD: 4x Western Digital Caviar

DVD: NEC DVD burner
a c 144 ) Power supply
a c 156 V Motherboard
August 21, 2010 6:25:47 PM

Work through our standard checklist and troubleshooting thread:
I mean work through, not just read over it.

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

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:

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:
At this point, you can sort of check the PSU. Try to borrow a known good PSU. 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.

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.
August 21, 2010 7:35:11 PM

Good info. I should buy case speakers first and I'll see what I can do from there. THANK YOU