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Computer doesn't turn on

Last response: in Systems
May 3, 2012 11:36:49 AM


I assembled a new computer about a month ago. Had an issue a week ago with having to clear CMOS on the sabertooth x58 motherboard. Now, after shutting down the computer down last night, it won't start up (no response after pushing the power button). The onboard LED light is on indicating the motherboard is getting power. None of the fans (including CPU cooling fan) turn on. None of the on board indicator LEDs turn on. I disconnected and reconnected 2-pin PWRSW connecting to the case's front panel. No action.

Any advice in further troubleshooting will be much appreciated.

More about : computer turn

May 3, 2012 12:22:01 PM

disconnect the pc from power and leave it for 2 minutes then try again
May 3, 2012 12:25:01 PM

Kand said:
disconnect the pc from power and leave it for 2 minutes then try again

unfortunately, that didn't work
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May 3, 2012 12:40:40 PM

check every connection on the MB, from video card to ram
it could happend that the video card or a ram module are out or their slots...
a b B Homebuilt system
a b V Motherboard
May 3, 2012 12:57:33 PM

There should be a power issue from what you´ve described -- it can be a faulty power supply. If it is a Corsair PSU have a look at it

Sometimes it can be a faulty case power button. Test it by trying inverting the power pin to the reset pin -- then start it from the reset.

Best solution

a c 122 B Homebuilt system
a c 156 V Motherboard
May 3, 2012 3:43:04 PM

The paperclip trick will work with any PSU, not just Corsair. The problem is that it can tell you if the PSU is bad (fan does not spin), but it cannot tell you if the PSU is good (fan spins, but PSU cannot power system).

Work systematically through our standard checklist and troubleshooting thread:
I mean work through, not just read over it. We spent a lot of time on this. It should find most of the problems.

If not, continue.
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.

Breadboard with just motherboard, CPU & HSF, case speaker, and PSU. Breadboard with just motherboard, CPU & HSF, case speaker, and PSU. At this point, if you do not have a system (internal case) speaker, you really need one.

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, LED's, or fan activity:

Check for line power at the PSU input. Extension cords, power strips, and power cords do fail.

If you have power and no beeps, suspect components in likely order are PSU, motherboard, and CPU.

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 green wire should read 5 volts and drop to around 0 volts while you press the case power switch.

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.
May 3, 2012 4:20:29 PM

Seems dead psu to me
May 11, 2012 3:19:40 PM

Best answer selected by batogrujanac.