This morning my computer wouldn't turn on. Pressing the power button has no affect. When I turn off the switch at the back and push the power button after turning it back on it seems for about half a second that everything works: fans appear to start moving and the PSU light turns on.
This happens only for a brief moment (less than a second) and then everything turns back off. I can repeat this by turning off and on the switch at the back of the case or by unplugging the power cable out and plugging in again.
There is a small LED on the motherboard which is always on when power is connected (doesn't matter if the computer is on or off) and it is still on now.
I am trying to diagnose what is the cause of the problem PSU or motherboard. Any ideas?