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PC powers up but won't boot. Not even post screen!

Last response: in Systems
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August 4, 2010 10:20:50 PM

Hi, a PC (Compaq/HP running Vista) I'm working on won't boot nor display the POST. Fans, HDD, etc power up but not a hint of any onscreen activity.
Monitor is good & display settings are fine.
Can access HDD using another power source.
Have tried motherboard in other boxes, nothing happens.
Tried with PCI cards...nothing.
Please help!
August 5, 2010 2:38:39 AM

Did it just stop working one day, or were you doing upgrades?
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August 12, 2010 8:16:32 AM

Thanks very much for the reply. It just stopped...apparently, that's the line the customer gave me. Very odd, I initially thought the graphics card had given up but...lost for answers.
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August 13, 2010 6:08:23 PM

dazzaman said:
Thanks very much for the reply. It just stopped...apparently, that's the line the customer gave me. Very odd, I initially thought the graphics card had given up but...lost for answers.

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.

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

The breadboarding thread has a paragraph about how to build and test a PC in stages.

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

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.

If no beeps:
At this point, you can sort of check the PSU. Try to borrow a known good PSU. 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.
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