I did the back probe a while ago on the 12 volt sata connector and it read fine so it may be another problem, I wonder is it possible the bios got wanky because if I bump the memory up to 1600 mhz (which it is rated at ) or xmp profile it also won't boot, goes into boot loop.
It's the +3.3v and +5v of power you want to check,.. first test pin-8 on the 24-pin ATX connector. If not within range,.. the system never sees the Power_Good signal and therefore does not start or run properly.
Intel indicated the decision to eliminate Kaby Lake compatibility with Z370 was due, at least in part, to requests from motherboard vendors that the company make a "clean split."
For motherboard vendors, this removes the burden of adding support for Kaby Lake (and requisite validation) during a time when most motherboard vendors are already stretched to their engineering resource limits due to rapid fire Intel and AMD launches.
Rumor is Intel will have Z390 motherboards coming out in 2018,.. that support enhanced IA and memory overclocking, Thunderbolt 3.0 w/ DP 1.4,.. and perhaps eight-core processors.
The 730T supports 360mm rad in top, but you will be into top drive bay.
A 360mm AIO cooler will be one of the best cooling solutions for 4790K,.. if it is adequate @ 5.0Ghz overclock depends on Vcore, ambient air temp, and CPU load,.. you will need to test and see what results you get.
You will want to connect water pump as per instructions,.. most likely to 12V CPU fan header.
If you have Arctic MX-4 on hand,.. I would use it. Otherwise the pre-applied TP would be fine.