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Boot-up after power outage

Last response: in Motherboards
December 15, 2012 3:46:32 AM

Hello all,
I have an Asus M378-EM motherboard on an Enermax FMA II power supply on UPS.
After the latest power outage and while the pc was shutdown, my wife got tired of listening to the UPS complaining and shut it off.
When I came back home, I turned it back on but the PC wouldn't power up.
Since the MB had power (the LED was on) I assumed there was nothing wrong with the PSU.
After a few trials I took out the PSU and powered it on by bridging the green ATX connector cable.
After that success I turned my attention to the MB.
No matter what I did (taking it off the case, attaching the bare minimal components etc.) it wouldn't fire up
What I did next was to put everything back together, bridge the ATX connector and use the PSU power button to turn it on.
I have yet to figure out what goes wrong in this system and for the past couple of days using the paper clip solution, which sooner or later is bound to fry something.
Any ideas for what to try next?
Thank you

More about : boot power outage

a c 150 Ĉ ASUS
a c 559 V Motherboard
December 15, 2012 4:29:30 AM

Try starting the board by shortly connecting together(use a screwdriver or similar) the 2 pins on the motherboard corresponding to the case power switch.
a c 122 Ĉ ASUS
a c 481 V Motherboard
December 15, 2012 5:23:37 AM

if the system was in sleep mode it may be locked up..have you tried clearing the cmos??
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December 16, 2012 4:00:30 AM

alexolu, It's probably the first thing I tried without success.
Smorizio, it was properly shutdown for certain and clearing the CMOS is one of the things I did when I had taken it apart.

When I took it apart, after clearing the CMOS I rebooted, went again into bios and took the paper clip out (yes, while working). I then turned it off by the power switch.
Thinking I solved this, I put it back together, but again it didn't work.
I now think this is either a choice in the bios, or something in the MB that doesn't like been without power (bios again).
Does anyone know how the power switch works in conjunction with the atx PS_ON# pin?
a c 122 Ĉ ASUS
a c 481 V Motherboard
December 16, 2012 5:52:46 AM

the power switch on a case is just a standard switch it lets the 5v flow from the power on lines into the mb. check to see if your case has a small daughter board for the on switch and usb ports.sometime it a lose cable or the daughter board goes bad. if not check the voltage of the power supply before you green wire it. make sure you have 5v on the power good line. i would see if a friend had another power supply to test with.
December 23, 2012 2:55:37 PM

I finally took the paper clip out while working and it didn't power off. Since then it's working flawlessly. Until the next power outage...