Hi All,

My Optiplex 760 does not turn on. When I press the power button, a green 3 LED light comes on. It disappears when I let go of the power button.

It seems a 3 means it's a possible motherboard error. Nothing on the mother board looks abnormal. No burnt smell. The amber light is on when the power is plugged in.

I tried disconnecting all USB-connected devices, and even the monitor, then I pressed the diagnostic button on the back of the PSU and the green light comes on. Does this confirm that the prob is the motherboard? Should I still bother to disconnect and check the different memories and cards one by one?

In the days prior to the computer dying I did get some warning signs. For example, the computer would go to a deep sleep on its own even though I set the power setting to never sleep. Another thing is that a few times when I press the power button (after shutdown), the computer would sound like it was starting but then it would go off after like two secs. Then I would have to press the power button again before it would boot up.

Wondering if you ladies and gents would know what the likely cause is based on my description?