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Built new PC but shorts out 1-2 seconds after booting

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December 25, 2010 5:46:30 PM

Just finished building my new computer but when i turn it on it shorts out right after. Tried unplugging all unnecessary wires but it still does it. Have double checked that all wires are plugged in correctly. How can i find out what part is causing the problem?
December 26, 2010 1:40:37 PM

I read through that but still dont know what the problem is. I think it is either the motherboard or processor that is broken but i don't know how to figure out which one to get it replaced. How can i narrow it down. All that is connected now is the motherboard to the powersupply with the processor in place and 1 stick of RAM, but it does the same thing just turns on for a second and shorts out. How can i determine which exact piece is causing it
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a c 104 B Homebuilt system
December 26, 2010 1:43:19 PM

Is it still in the case or on the table? If it is in the case it can be shorting to the case (did you use the standoffs?) on the table most likely bad board.
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a c 122 B Homebuilt system
December 26, 2010 1:45:22 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.

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.

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...

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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March 2, 2013 9:50:27 AM

i am having the same problem i bought a new psu and my system goes on for literally 1 second the front fan turns slightly and the cpu fan there is a red led and a green led that is constantly on there is no beeps at all i have read and tried everything on your trouble shooter but still i can not identify the problem.

My specs are as follows

xfx geforce 8200 mother board
amd athalon 64 x2 dual core
ati radion 4670 gpu
600w atx alpine silent psu
1x kingston 2gb ddr2 ram
1x ocz tech 1gb ddr2 ram
2 system fans

i have replaced my psu and literally took my system apart to nothing a rebuilt it using your check list and the xfx user manual trying with just basic hardware connected ie cpu 1 stick of ram gpu i have tried it every way but it is still the same no matter what i am starting to think it is either the MOBO or the CPU is there any way to know what i need to replace without it costing me money to find out
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