Your Power supply seems to check ok, since your motherboard turns on a green light. If you can confirm this by testing it on a different machine that would be helpful.
It must be either your CPU or faulty motherboard, going in that order.
PLEASE MAKE SURE THAT YOUR CPU 4pin power cable is connected. This case being X. Without this there is no chance of your system doing a POST(power on self test)
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Please confirm that
A, C, M, X
are all fully connected.
Unplug your computer from the wall, hold the power button. If your power supply has an on and off switch in back please turn it off and then back to on. Then plug it in back into the wall and try and power on.