Disconnect power and all pripherals including the mouse and keyboard. Press and hold the power button down for about 30 seconds. Let go and then connect to power. Do not connect any peripherals yet. Ensure the power supply LED at the rear is lit and try powering up.
If the LED at the rear is not lit, its a power supply fault. Otherwise, its a motherboard failure.
Thanks for the suggestion a few years back due to a fan failure I changed power supplies. My current power supply a evga 600 does not have a light. As I said the mother board did light up though after pulling everything. It would seem that I found the cause my current graphics card when connected prevents the computer from powering up. If I unplug the card from the power supply my fans come on and it seems the computer will try and boot. So I am ordering a graphics card.