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Computer starts but no display on monitor

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Last response: in Systems
January 5, 2011 3:24:22 AM

Hi guys, I have a custom built PC I had done for a client, the client is a close friend of mine..
The system is fully assembled and all the connectors are connecting to where they should be and the CPU heatsink is in place.. although the first time I ran it one of the pins for the HS was a bit loose.. could I have cause the CPU to fry? I don't see any indication of it being so..

Anyways.. The computer runs, boots, but does not post nor show any display on the motherboard (which is an very old one).
The motherboard has a VGA integrated graphics card, so I decided to go out and buy one and test it out to see if it made any difference..
It didn't but I did find that the fan for the GPU was not spinning.. so could this be a motherboard failure instead? All the other fans are working perfectly fine.. I have switched out the ram, power cycled, took out the CMOS battery.. only thing I have in mind now is the HDD or the MB.

Should I buy a new one since the one I used in this build is quite old? (Approximately 5 years old..)

Just another thing.. There is a bright green led light on the motherboard which seems to indicated that its powered on by the PSU.. the HDD also seems to be showing a light and is powered on.. my motherboard gives me no beeps at all and the monitor shows display on my other custom built PC.

Please help! This is urgent! :hello: 

More about : computer starts display monitor

January 5, 2011 5:51:33 PM

Is the CPU supported by the motherboard? If you have new model CPU and old mobo, you might have to update the BIOS.

Since the mobo is old, it is better to get a new one.
a b B Homebuilt system
a c 122 V Motherboard
January 5, 2011 6:29:44 PM

If the CPU isn't the issue, pull everything out of the case and breadboard the rig.

Breadboarding 101:

1. Put mobo on a non-conductive surface
2. Install:
a. 1 stick of RAM
b. PSU
c. CPU/Heatsink assembly
3. Connect all necessary power cables to installed components, including the display cable to the VGA.
4. Using a flathead screwdriver, jump the PWR_SW pins on the mobo.

If unsuccesful, move the RAM into a different DIMM slot, and then try again until:
A. You've successfully POSTed - which will result with a message indicating no boot device found; or
B. You've used every RAM in every DIMM slot
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January 5, 2011 11:52:31 PM

My motherboard is held up by these little screws inside the case which is supposed to be a non-conductive mount. But i'm having a great feeling its the motherboard because the GPU fans wont spin but everything else works. That, or the PSU..
a c 121 B Homebuilt system
a c 156 V Motherboard
January 6, 2011 11:33:54 AM

If you cannot boot, nothing works.

Work systematically through our standard checklist and troubleshooting thread:
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.

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.

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.