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Trouble with CPU fan and video (no boot)

Last response: in Systems
December 31, 2010 7:07:13 AM

Hey guys I've recently built a new system and it's been acting really weird. When I first built it, I could not get the CPU fan to spin and there would be no video. I checked all the connections and press down on the connections. It then spun and I got it working. However, it randomly shut down and again, CPU fan stopped working yet again and I'm getting no video. What could be causing this? I've checked temperatures and they seem perfectly normal. Anyone have any idea what I could do to fix this?

I5 760
Corsair TX 750
Asus P7P55E LX Mobo
GTX 470 SC
Coolermaster 212+
Antec 300 case

a b à CPUs
December 31, 2010 9:43:17 AM

remove power from rear of cpu, reseat everything firmy (video and mem), make sure your video cards supplemental power input is connected, disconnect drive power/ribbon/SATA connectors, reset BIOS...

try again...

Your PSU or Mb 'ain't cuttin' it'! (If you remove the video card entirely, the MB should beep furiously that it can't find a video adapter...try that)
a c 172 à CPUs
December 31, 2010 11:54:57 AM

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.

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.
December 31, 2010 11:58:57 AM

If your motherboard is like my p7p55d then the only two power connections to the motherboard are the 24 pin power connector and a 6pin power connector.That which you're describing sounds like a loose cable.I'd press those down again and see if that works.If it doesn't,it could be either a malfunctioning mobo or a problematic psu.