Seems like a power issue, or maybe a faulty motherboard.
Start with checking your wiring, especially the front panel connector. Also make sure something is not making a short under the motherboard (lost screw for an example). Also double check the CPU is installed fine in the socket, with no bent pins. Check the CPU power connector is not reversed.
Then, try disconnecting every component one by one, and test each time.
Your CPU has integrated graphics so you don't need the graphics card to run a test. Cooling is also not needed for a quick test.
If you arrive at the minimum (power supply, motherboard, cpu and 1 ram stick) and it does not power on, best bet is the motherboard or power supply is faulty.
Try with another (verified) power supply, just for the test. If it powers up, problem is the power supply (it could happen sometimes).
If it still does not power up, remove the remaining ram stick, and power on. If it does not make some beeps, then your motherboard is faulty.
Nice rig you have there !
Disclaimer : computer repairs is my day job