[gijoe77]

I've been doing a lot of work with my various o2's recently, and I've come across this failure-to-power-up a bunch of times already. Here are some steps I took:

very important: step 0: NEVER PULL THE MOTHERBOARD WHILE THE POWER CORD IS PLUGGED IN
step 0a. when you pull out the power cord, hit the power button to discharge the CAPS in the PSU, only then move on to the below:
1. Reseat the PSU - do this a few times
1a. take out all components and blow off the dust (canned air is ok, air compressor is better I guess, just don't go too crazy)
2. set the PWR jumper, power on, unset the PWR jumper, power on. you can leave the PCI slot out, its not needed in there. Do this a few times. I've had o2's that wont power on when you set the PWR jumper, but will once you take it off.
3. reseat the CPU. do this a few times, you might have to do step 2 and 3 a few times.

I've had o2 motherboards that I was sure were dead (I have about 7 o2's right now so I've been swapping parts left and right), some started working after 15 tries...

also, make sure your grounded/discharged from static buildup when handling these boards. at the very least touch the metal frame for a good 2 seconds, then pull the boards and start handling them

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Thank you, Raion.
After I set "PWR UP" jumper, I can use the O2, but the machine work as soon as I plug in the power cord. The PSU is OK. Please help me to fix.

ok so if it powers on, what is the issue your having now?