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I've been trying to fix a desktop pc which doesn't heat up the processor (not getting connection to) during boot up/pressing power on button. This has occurred before and removing all components and adding them again has fixed it twice but I need to know what might be causing this or which part/s may be faulty and prevent it from hapening again. The processor is a Intel p4 2.8 Ghz. Motherboard: Intel Desktop Board D865GSA

When the system isn't working, when pressing the power button, the fans rotate but the system turns itself off after a couple of seconds. I tried removing the heatsink and touching the processor but there doesn't seem to be any heat generation. I've tried other PSU once but it didn't help.

I suspect something on the mobo has malfunctioned or something. Any help would be appreciated?

EDIT: i'm not implying why the processor isn't heating up if the mobo is running. I'm asking what might be stopping the connection to the processor to stop it from running in the first place.

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    'Heating up' isn't a good indication of anything. Are there any other issues? Bios error messahes or beeps for example?
    – Journeyman Geek
    Oct 31, 2014 at 7:03
  • processor does have to heat up for the system to work. That is why computers need heat sink. My problem is that it isn't doing so. Oct 31, 2014 at 7:05
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    You're mixing up cause and effect. The processor produces heat because its working. Usually issues with systems have other symptoms - the POST is meant to catch those. Your problem is unlikely to be due to lack of heat production, and usually your system wouldn't heat up that fast/
    – Journeyman Geek
    Oct 31, 2014 at 7:06
  • sorry, i'm a little confused. the system doesn't boot to bios, and no beeping sounds too. I'm just asking what's the cause of this. Oct 31, 2014 at 7:08
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    Heat gets generated because the processor has an electrical resistance. If it really doesnt heat up, it doesnt get an electrical current. I'd check capacitor rot and the voltage of your PSU output. Maybe the PSU has gone bad.
    – agtoever
    Oct 31, 2014 at 8:06

1 Answer 1

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The moment you turn on the computer, your CPU should start to work and to generate (dissipate) the heat. If your CPU is cold, this mean that it is not powered. No power to your CPU, no BIOS, no beeps... nothing :) The fact that system turns off after a few seconds is usually the CPU overheating issue as motherboard will cut the power to prevent overheating. Since you've checked this, and your CPU is stone cold, I would try to shed some light on how you can troubleshoot this issue. I don't have exact insight in your situation and it could be that you are misinterpreting something or you just didn't put all the facts on the paper, so I will try to give you some steps just to be sure that you have exhausted all your options before you give up:

  1. Check the voltages of your PSU when you turn on the PC. You should have 12V (+/-10%), 5V and 3.3V in +-5% tolerance range. Even having a little bit less than what tolerance range allows should be still fine. Try to borrow a known good PSU. It wasn't once that "I have found another PSU to try" , ends up with "Is it possible that both PSUs are bad?".
  2. Check the voltage of your CMOS battery. A dead battery could indeed be the culprit. I've had numerous issues with customers PCs. The light would come on and the fan would spin for a second and then nothing. Replacing the system battery and the system booted right up, good as new.
  3. I have also seen the issues with the extra standoffs below the motherboard that are causing a short and prevent the system from booting. Sometimes, it takes just the small movement to cause short or unshort. I have seen the systems running for years like this, and suddenly went into the state similar to yours
  4. If the voltage regulation that surrounds your CPU on the Motherboard looks fine, try with another CPU. I have had a chance to see that, probably due to malfunction of the thermal sensors (which actually is specialized thermal diodes) in the CPU, PCs turns off similarly as in your case.
  5. When you are doing this, check for any bent pins
  6. Finally, if nothing above doesn't work, you may have ended with the faulty motherboard

At the end, I suppose that you have plugged in the 4-pin CPU power connector located near the CPU socket. :) :)

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  • +1 for PSU and just to add, if your CPU socket has bent pins it can also cause this behaviour - get a good torch and just make sure there's no out of place/bent pins
    – Fegnoid
    Oct 31, 2014 at 8:48
  • @Fegnoid - You might want to provide better instructions then putting a torch to a CPU.
    – Ramhound
    Oct 31, 2014 at 9:22
  • Using an acetylene torch will certainly heat up the CPU. :)
    – Hennes
    Oct 31, 2014 at 9:27
  • Sorry - I meant as in light (superbright LED ones tend to be good) not acetylene, but that would heat up your CPU :)
    – Fegnoid
    Oct 31, 2014 at 9:58
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    UK torch == US flashlight... though I love the possible misinterpretation ;-)
    – Tetsujin
    Oct 31, 2014 at 10:30

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