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Computer will not power on

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Anonymous
September 14, 2010 6:53:12 AM

I have tried everything I can think of including going through the 'list of things to try' post linked to in this forum.

My system will not power on, no fans, lights, nothing. I placed a wire between the green and black wires of the PSU 24 pin connector to the motherboard and when I did that it worked and the fans ran. So I do not think the PSU is the problem.

I have tried turning it on while sitting on top of a table with minimal parts connected (just the psu, motherboard, cpu, cpu fan) and nothing happened. (also tried plugging in the video card and memory, did not help, although I am under the impression that they dont need to be in if all you want to do is turn the thing on).

I looked carefully at the socket, all the contacts appear to be in good shape, none are bent or anything.

My mother board is a gigabyte p55a-ud3. My cpu is an i5 760, the fan is just the stock fan that came with the cpu. My power supply is an OCZ 700W ModXStream Pro Power Supply.

Any ideas?

More about : computer power

September 14, 2010 7:27:56 AM

one thing that i would say, and do this at your own risk is jumping the pins that your case power button attaches to for a second and seeing if it turns on. i was building a pc for a buddy last month and his power button on his case was dead so we just moved the reset connection to the power pin and problem solved.
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September 14, 2010 2:19:40 PM

Work through our standard checklist and troubleshooting thread:
http://www.tomshardware.com/forum/261145-31-read-postin...
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.

I have tested the following beep patterns on Gigabyte, eVGA, and ECS motherboards. Other BIOS' may be different.

Breadboard - that will help isolate any kind of case problem you might have.
http://www.tomshardware.com/forum/262730-31-breadboardi...

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:
http://www.cwc-group.com/casp.html

Make sure you plug the CPU power cable in.

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

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.
http://www.youtube.com/watch?v=5FWXgQSokF4&feature=yout...

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. 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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