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Problem When I Plug In 4 pin ATX 12V

Everytime i plug in the 4 pin ATX 12V the comp boots up for 2 seconds and keeps shutting down.

When i remove the ATX 12V the comp seems to boot up and stays on, all fans going.
tried with just running power supply, cpu with heatsink, but everytime i switch it on it cuts off after 2 seconds.

No post beeps. Power supply is checked and changed as well.
4 answers Last reply Best Answer
More about problem plug
  1. System specs?
    Specs on both PSU's?

    Without the CPU poer plug, a PC will not boot.

    Sounds like either a bad PSU or motherboard.

    Our standard checklist and troubleshooting thread:
    http://www.tomshardware.com/forum/261145-31-read-posting-boot-problems

    Our standard checklist and troubleshooting thread:
    http://www.tomshardware.com/forum/261145-31-read-posting-boot-problems
  2. System specs:
    Gigabyte GA-8IR2003
    Intel Celeron 1.8 GHz
    PSU : 400w and 500w

    I am sure that the PSU is not bad. Because i have already changed the PSU and checked the voltage reading of yellow and red wires through multimeter.

    BTW my one is not a new build PC. Its running from 2003 onwards and all of a sudden this happened. So is it for a bad CPU or motherboard. Any way to be sure of it? Is there any chance that a bad CPU would resist the motherboard to supply power??

    Thank You
  3. Best answer
    Have the same problem on an ECS P4M800-PRO.

    Plug in ATX_12V (4pin) with the ATX2.x 24pin and computer boots for 1sec and dies. Disconnect the ATX_12V and the computer powers on, but does not go into POST. Previously, computer was running fine until it needed a windows update--it auto-rebooted and died. Was a CCTV server with about 2 yrs uptime.

    Just replaced it with an Biostar board and it POSTs & boots. So, conclusion was it was the motherboard--likely the regulators were shot. What I hate was I had a 3.2Ghz PentiumD (was nice), and thought it was the CPU, so I got a cheap Celeron E3200...somewhat a waste since it appears the CPU is good. Also, the old MB had DDR ram, and the new MB only uses DDR2 ram--so it's off to the shop again :( Also, my nice AGP integrated graphics is now a paper weight since the new board as no AGP, but PCIe ... ugh. Oh well, it's going to be another $40+DDR2 memory to fix this problem...

    Lessons learned:
    + Check P/S leds for voltage. Also if you ethernet light comes on, PS is likely ok.
    + If you can POST but no boot, it's memory or CPU (remove then and see if the bios reports the right errors)
    + If you get no POST/Beeps, it's the MB--even if it powers up, it's still the MB.
  4. Best answer selected by r_manic.
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