Sign in with
Sign up | Sign in
Your question

Computer boots but POST fails

Last response: in Motherboards
December 10, 2011 2:40:13 PM

I just replaced the AMD heatsink that came with my Phenom II X4 with the Cooler Master Hyper 212+. when installing it, I cam across a few problems, the most alarming of which was the CPU popping out of its place despite being locked in. Since my case is not very big, I had to remove my motherboard to put in the new heatsink. Once I finally reassembled everything, I booted up and all the fans started, yet nothing came up on the screen. The computer was working fine before I changed the heatsink. I don't know what to do to fix it. Did I break my CPU? Thanks for your help.

AMD Phenom II X4 955BE
AMD HD 6770
4GB Kingston DDR3 1333
Cooler Master 550W GX
a c 194 V Motherboard
a b À AMD
December 10, 2011 2:48:36 PM

Get the pin alignment right ?

Remember to plug in CPU fan, 8 pin EPS or 4 pin CPU cable ?

Plug the GFX card cable back in ?

Set all BIOS to defaults and conform CPU / RAM settings ?
a c 156 V Motherboard
December 12, 2011 4:47:57 AM

Actually, the computer cannot boot until the POST passes. :) 

Changing a heatsink should not affect system operation, but it is worrisome that you popped the CPU out off its socket.

Follow Jack's suggestions. If they do not work, it is time for more advanced troubleshooting.

The following is an expansion of my troubleshooting tips in the breadboarding link in the "Cannot boot" thread.

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 (standby power supply): 5 volts always on. The green wire should also have 5 volts on it. It should go to 0 volts when you press the case power button, then back to 5 volts when you release the case power switch. 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.

After that:
(Part of my standard troubleshooting supply)

December 12, 2011 6:55:32 AM

Alright, so I checked CPU again and realized that one of the pins is missing, which renders the CPU useless now, I think. Another problem though, is I tried reseating it and locking the socket, however the locking didn't seem to do anything because I could just pick up the CPU form the socket. Is this because of the missing and bent pins on the CPU or is the socket broken too?