Doby

Try the bench test, lay the board only on a piece of cardboard and connect only

psu
cpu with fan&heatsink
video card
1 stick ram
mouse,keyboard, monitor
Case speaker

Clear the cmos, make sure the computer is unplugged from the wall outlet when you do, read your manual on how to do this.

Check all jumpers are set correctly, again the manual will explain these.

Make sure the aux 12V from the psu to the motherboard is connected.

To start touch the 2 pins that the case switch is connected to with a screwdriver.

This will eliminate the possibilty of a case short and also only uses the necassary components to let the computer pass post. Try it and let us know if the computer will then post