System will not power up. Endless loop of On/Off cycles every 2/3 seconds.

By pepperchu
Nov 30, 2004
  1. I'm new to this forum so be nice.

    I have a ASUS A7N8X board with a Allied AL-A400ATX power supply. Starting this weekend, with no notice, my system will not boot up. Instead, it seems to be stuck in a On/Off loop. I can't get into bios, safe mode or use my bootup floppy because the cycle doesn't last long enough to reach that part of the startup routine. The front On/Off switch does not work. I have to power down by using the main power switch on the Power Supply. I think I've narrowed it down to my power supply or my motherboard. I tried a new hard drive . . . no change. After disconnecting all my various drives including hard drive(2), CD, DVD, and Floppy; I am still getting the On/Off loop. The power supply seems to be automatically turning itself on/off. Even when I disconnected the On/Off switch cable from the motherboard it continues. I looked at the capacitors on my motherboard and there appears to be no sign of bulging or discharge. Do you think I should try to replace my power supply? or motherboard? or something else? I'm getting in a little over my head, but don't think I'm ready to buy a whole new system. Please advise.
  2. howard_hopkinso

    howard_hopkinso TS Rookie Posts: 24,177   +19

    I would definitely try a new psu first.

    Regards Howard :grinthumb
  3. pepperchu

    pepperchu TS Rookie Topic Starter

    You were right

    It was indeed the power supply. Replace it with a COOLMAX CMAX 400WCX-400B BK RT replacing the defective Allied AL-A400ATX 400W. Everything powered up just fine after the repair. Thanks you your help.
  4. LunisticTweak

    LunisticTweak TS Rookie

    what if replacing PSU doesn't work

    i stripped down my system to Soyo Dragon 2 PLUS mobo, Intel PENT 4 CPU, and Ultra V series 500watt ATX PSU. the PSU is the new one, but i still get the 2-3 second boot up, then shut down. only time it continues to run the PSU and the fans is if i disconnect the 12V 4 pin CPU plug-in and only have the 20 pin connection plugged in. then it "runs", but w/ no display on the monitor.

    i've had this system for over 4 years and it's never given me any trouble till a couple days ago.

    thanks in advance
  5. Tedster

    Tedster Techspot old timer..... Posts: 6,000   +15

    DO NOT hijack threads. Start a new one.
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