Hello mate
Sorry to hear about your problem with the power up.
PSU is a good place to start. While you wait could you inspect each and every connector, occasionally the wires will pull out of the metal inserts.
One other thing please check that your motherboard is mounted correctly and that there are no contacts that cause cause your system to short out. Easy way to test is to take your motherboard out of the case and lay it onto of the box it came it. If it powers on then inspect your case there might be a visible clue as to where or what is causing the contact (short).
Let us know how the PSU worked out.
To help us help you - please provide as much information about your system and the problem as possible.