PC turns off randomly, mid boot or after running for hours.

Configuration:
Processor- Intel Dual Core E5700
GPU- Internal
Cooler- Stock Intel LGA775
RAM- 2GB Kingston 1333MHz / 2GB EVM Dynet 1333MHz
Mobo- Gigabyte GA G41M Combo
HDD- Seagate Barracuda 500GB
PSU- 400 W Circle Power Supply
Case: Some generic no brand case
OS- Windows 8.1 64 Bit

Have run with this config (except the new PSU) for a couple years without issues. For the past one month my PC has been randomly turning off without warning or BSOD. Sometimes while booting and after running for hours at other times.

What I have tried so far:
1. Replaced the old PSU with leaked capacitors with a new one.
2. Replaced dead CMOS battery.
3. Cleaned the heatsink and re-installed it with new thermal paste. (Temps normal now while idle ~40 deg c and under load ~72 deg c)
4. Reseated the Processor.
5. Tried one RAM stick at a time and both.
6. Checked the PSU voltages. Fan runs normally with Green and Black pins shorted. Here are the readings: All Orange Pins: 3.39v, All Red Pins: 5.37v, All Yellow Pins: 12.19v, Gray (Pin 8): 5.35v, Purple (Pin 9): 5.25v, Blue (Pin 14): -11.62. The Red pin voltages have me a little worried because according to this article the max voltage for Red pins is 5.25v.
7. Tried breadboarding. PC ran fine for few hours but it runs fine for a few hours in the case as well. So I think breadboarding was inconclusive.

The BIOS speaker beeps once while booting which indicates all is fine with my Award BIOS. One of my mobo standoffs is missing but I put a cardboard between the mobo and case, so I don’t think the mobo is shorting on the back. Also cleaned the mobo as much as I could. I have no overclocks or under volting. There seem to be no loose screws lying around. All cables are plugged in properly. Another thing worth noting is that once it turns off, pressing the power button on the case won’t start the PC. I have to unplug the PC from the wall socket and plug it back in before it can turn on.

Someone help me out here. If more info is needed I'll add it.
Reply to magnabolt
7 answers Last reply
More about turns randomly mid boot running hours
  1. I would look at that psu first. Not on the Tom's tier list at all.

    How did the previous psu die?

    There are also vrms on the mobo and they could be getting iffy given their age. Might look closely at the mobo.
    Reply to J_E_D_70
  2. J_E_D_70 said:
    I would look at that psu first. Not on the Tom's tier list at all.

    How did the previous psu die?

    There are also vrms on the mobo and they could be getting iffy given their age. Might look closely at the mobo.


    The PSU is from a local brand, but one of the good local brands. You wouldn't find it on Tom's list though.

    The old PSU didn't die suddenly. PC started randomly shutting down like I said, which is when I suspected the PSU was dying. So I opened it to find a couple of leaked caps on the input side.

    The mobo is quite old and I have used it a lot over the past years. What should I exactly look for on the mobo?
    Reply to magnabolt
  3. Just google "leaking motherboard capacitors" and look for any discolored areas around any of the chips.
    Reply to J_E_D_70
  4. J_E_D_70 said:
    Just google "leaking motherboard capacitors" and look for any discolored areas around any of the chips.


    All caps look fine.
    Reply to magnabolt
  5. I had this problem with one of my builds, and after checking thoroughly I noticed that I forgot to plug the cpu power. Even after I plugged that in, the pc never stayed on for more than a minute.

    NOTE! It was working before I messed around it.

    I think I damaged the cpu or the mobo because neither would work afterwards even with different components.
    Reply to Samuel_gaming
  6. Samuel_gaming said:
    I had this problem with one of my builds, and after checking thoroughly I noticed that I forgot to plug the cpu power. Even after I plugged that in, the pc never stayed on for more than a minute.

    NOTE! It was working before I messed around it.

    I think I damaged the cpu or the mobo because neither would work afterwards even with different components.


    I don't remember starting without plugging in the CPU power. Now only if I could get a spare working power supply to test with.
    Reply to magnabolt
  7. magnabolt said:
    Samuel_gaming said:
    I had this problem with one of my builds, and after checking thoroughly I noticed that I forgot to plug the cpu power. Even after I plugged that in, the pc never stayed on for more than a minute.

    NOTE! It was working before I messed around it.

    I think I damaged the cpu or the mobo because neither would work afterwards even with different components.


    I don't remember starting without plugging in the CPU power. Now only if I could get a spare working power supply to test with.


    For me it wasn't the power supply, it was either the cpu or mobo. I tested the power supply on a different build and it still works. It also might be the operating system or hard drive failing
    Reply to Samuel_gaming
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