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Computer Won't Turn On

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February 5, 2011 3:51:26 AM

Hello,
I recently built my own computer (using the case, ram and power supply from an older one). I have everything in place; all the power cables are inserted in the correct places, the power supply works fine, the ram fits perfectly, but it does not turn on! The green light on the motherboard is on, but that is the only sign of life in the entire computer. I've already tried switching out power strips, power cords, and ram sticks, and I've also tried taking out the video card. The hard drive, processor, and motherboard are brand new.

Here's my specs:
ASUS M4A785-M motherboard
Western Digital 500gb 7200rpm HDD
AMD Phenom X4 9850 Quad Core Processor
305w functional power supply

Thanks in advance!

More about : computer turn

a b ) Power supply
February 5, 2011 10:22:19 PM

If you don't even get to the BIOS, can't get the PSU and fans to start spinning, make sure the POWER and RESET switches are plugged in correctly. If you get past that, then try some breadboarding (look that up on this forum for a pretty good walkthrough).
February 6, 2011 3:47:32 AM

I'm new to this kind of stuff; could you explain to me what the power and reset switches are? are they on the motherboard?
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February 6, 2011 8:33:13 AM

You should be able to find that in the instructions. The "power button", the "reset button", hdd leds from the box etc all have cables that you need to connect to the mobo. They have very small black edges.

Is reset necessary? I find the power button sufficient for testing purposes.

ps: I think that for the power button doesn't matter is text is up or down.

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a c 122 B Homebuilt system
a c 144 ) Power supply
February 6, 2011 11:19:44 AM
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Work systematically 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, 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.
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.
a b ) Power supply
February 6, 2011 12:52:40 PM

FATAARDVARK said:
I'm new to this kind of stuff; could you explain to me what the power and reset switches are? are they on the motherboard?

the switches themselves are on the case (the POWER ON and RESET buttons). They plug in the mobo in a designated connector, usually along the HDD activity LED, it differs slightly from mobo to mobo. You can refer to the mobo's documentation, or if you don't have the booklet anymore, on the mobo's manufacturer website.
February 17, 2011 5:53:18 AM

K thanks for your input, guys. I found out that the whole time the only problem was that the power switch was plugged into the wrong port. There was a connection that fit the power switch perfectly, but it was the LPT port.
*sigh* I'm such a noob with computers. :( 
February 17, 2011 5:53:52 AM

Best answer selected by FATAARDVARK.
a b ) Power supply
February 17, 2011 8:27:35 AM

This topic has been closed by Maziar
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