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Custom built computer over a year old won't turn on.

Last response: in Systems
December 10, 2011 2:24:08 AM

I have a computer that was working fine yesterday. I had to turn it off an unplug it temporarily to work on another computer and when I plugged it back in it won't turn back on. I have not changed anything in the system or altered which plug is used. The motherboard's power light is on but when I push the power button on either the case or the motherboard itself I get nothing. I hear no beeps, no case lights come on or even the motherboards CPU temp monitor. Computer has a 700w PSU for an i7-960 Overclocked CPU, GeForce GTX 460, 12GB DDR3 1600, a 1TB WD Green (please no comments on the cheap hard drive lol), and an 24x DVD drive. As I said though it was working yesterday and can't figure out why it isn't today. Any help or advice would be appreciated. Oh BTW...I have made sure it is plugged in and that the PSU is switched to the on position.
a b B Homebuilt system
a c 229 V Motherboard
December 10, 2011 2:48:34 AM

It could be the PSU. Since you have another computer, could you test it?

Best solution

a c 122 B Homebuilt system
a c 156 V Motherboard
December 10, 2011 2:51:30 AM

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.

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 (standby power supply): 5 volts always on. The green wire should also have 5 volts on it. It should go to 0 volts when you press the case power button, then back to 5 volts when you release the case power switch. 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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December 10, 2011 3:14:15 AM

Ok, uh, no offense moderator but I'm looking for a bit of an alternate solution. I see a whole lot of talk there about crossing wires and shorting power supplies with a paperclip...not something I am even remotely considering doing with a system that cost me almost $2000.00 when I built it. I have faith in my skills but hat just sounds a bit insane to me. GhislainG, thanks I will definitely try switching out the PSUs and post my results.
December 10, 2011 5:23:16 AM

Alright so going against my more cautious nature, I disconnected the PSU and using a small piece of wire connected the green and the adjacent black wire. The PSU turned on instantly and after triple checking that it functioned properly I reinstalled it into the case and connected the motherboard and CPU cables. Nothing. The motherboard still shows the blue light that tells me it is getting power. I wonder if the CMOS battery could possibly be the cause of the failure to boot? I don't get any POST beeps or anything when I try to start the power up. I can't understand why this computer has been working for over a year and just suddenly stop when all I did was shut it down and unplug it for a day.
December 10, 2011 8:21:39 AM

Took the Corsair 620w PSU out of my second computer and hooked it up to the old computers mobo and CPU. It booted fine but beeped a few times due to my hard drive and video card not being powered I'm sure. 620w PSU can boot farther than the 700w can. I'm going to go out on a limb here and say my PSU has gone bad. That'll teach me to stick with name brand instead of Rocketfish. Ugh! Thanks to GhislainG and jsc for your suggestions. Buying an Antec 620w, single +12V rail, output of 3.3V@24A, +5V@24A, +12V@48A, -12V@.8A, +5VSB@2.5A. Hopefully that should cover it.
December 17, 2011 12:29:30 AM

Best answer selected by independent8705.