see if there is a power light on the Mobo. Check plug socket for current if not, also change power cable and check again. Check that the power button on PC hasn't been damaged (you should here it click when you press it)
Disconnect everything from the Motherboard except the 20/24 pin Power and the Processor power. Turn off the power switch on the back of the PSU and hold down the power button for 10 secs. Turn the power switch back on then press power button. If nothing happens...
Swap out PSU. Carry out the same test. If it is still dead, that usually means there is something wrong with the motherboard.
If power does come back on and you get the PC to POST, start adding devices back on one at a time. If it falls over again, disconnect that device and try another one. This way you'll see if it is a device causing your issue, or if it keeps falling over randomly regardless of what you have plugged in, then it's probably the board.
This thread is now locked and can not be replied to.