Desktop Computer Powers On Then Shuts Off Instantly (After 1 second)?

Question

Hello,
I am having an issue where as soon as I power my 6-year old computer on, it shuts off after 1 second.
Then, it attempts to turn on again, but shuts off again, and the cycle continues until I hold down the power button.

I removed all USB devices, all PCI/PCI-e devices, all SATA devices, all fans (but the CPU fan/radiator), one RAM module at a time, and the issue still continues.

I suspect that the culprit is the power supply. I shorted pins 15 and 16 (power supply stayed on) then used a multimeter to check all voltages, and they are all within acceptable range, but I have my doubts about whether it means the power supply is fine (as there is no load).

Leading up to this, in the past month, my computer has restarted by itself without explanation once or twice a day.

Unfortunately, I do not have any spare computer parts lying around, and I'm pretty isolated where I am right now.

Should I take a gamble and order a new PSU, or could it be another part that's causing the issue?

What other tests should I try? As a matter of fact, could it be the CMOS battery (no data lost after startup, so I personally doubt it)?
About 10% of the time, the computer does start up successfully, either on first "attempt", or after a few attempts.

Thanks

Answer 1

Yes I had the same Problem, swap out CPU, same issue, swap out Motherboard, same issue.  So I took out the Motherboard, and took it up to local computer shop, they say cheaper to get new computer with the latest Intel CPU, so in week from now I get new computer!

Answer 2

- Verify that the power supply voltage switch is set correctly. - Make sure you are keeping the computer cool enough, - Check for causes of electrical shorts. - Test your power supply. - Test the power button on the front of your computer's case. - Reseating will reestablish all of the connections inside your computer which may have wiggled loose over time.

Answer 3

It sounds like it could be a bad power supply or even possibly a motherboard problem.

Answer 4

Check ALL the FANS.   Case FANS, is it running?  Processor FANS, is it still running?   Do you use Liquid cooler?   is it dead?  check check check.  

Answer 5

Most of the symptoms you describe are a typical PSU fault

when pin 16 goes low as you have simulated that tells the PSU to come on. This is normally done by the power switch and motherboard logic.

If everything is o.k the motherboard sends back a Power O.K  signal to the PSU to keep it running so could also be a Motherboard problem. The easiest part to prove is the PSU however the other symptoms you describe are a bit worrying and may point to the Motherboard more. As the PSU is easier and cheaper prove the PSU first

Answer 6

Likely overheating. Open it up & clean out the dust for a start.

Answer 7

Take board out of case, then try powering it up.  You might have a short to ground.  The "crowbar" circuit cuts the power off in the PSU when a high current surge on power up tells it to do that.

If out of case board and PSU run normally, you have some contamination that is shorting out the power.  You say you replaced stuff before.  Might have dropped a metal bit somewhere that is doing this problem.  Or a wrong screw position through board might be making a short circuit.  Nylon standoffs or screws would solve that.

On strange self-starting, and also on previous failures to start might point to PSU failing.  Get another of proper size or larger, not costly.

I have been building PC boxes for a few decades.  No problems yet like yours.  Once in my old VW bus I replaced the points in the distributor with a magnetic sensor.  At certain positions of the spark advance, the distributor arm would short to a too-long screw shaft in the side of it.  Freaky.

Answer 8

I forgot to mention that most of the parts have been replaced ever since in the last 1-2 years, except for the Motherboard and Power Supply.

Answer 9

If I were you would buy another, Sometimes you fix one thing and break another. he is already old.