This is a brand new build - everything except the case is new.  I have not been able to complete a POST cycle.  Equipment list is below.  I've built all of my home systems since Intel came out with the 486, and this behavior is new for me.  Behavior is as follows:
 
1.  When I turn on the external power switch for the PSU, the system begins a POST.  This is true even with all front panel connectors disconnected, so the front panel power switch pins on the motherboard are not being jumped.  There is no video output.  Fans spin up.  Motherboard lights come on.  No drives are connected.  No cards are installed on the board. 
 
2.  POST codes display on the board.  After 10 seconds or so the POST code hangs at '18,' which comes back as "Pre-memory North Bridge initialization is started."  After 30 seconds or so of being hung at '18,' the system power cycles itself and repeats the process, hanging again at '18.'. 
 
3.  The on-board power button has no effect on any of this.  The on-board reset button causes the POST codes to restart at the beginning, from which they hang again at '18.'
 
4.  I have four DIMMS.  Results are the same with all four, or with any two in slots 2 and 4. If someone would like me to try with one stick, please let me know which slot it should be in. 
 
Equipment (all new, so all is suspect).  Nothing has been modified except larger fan on cooler:
 
Z370 Classified K.  Hardware rev is 1.0.  BIOS version is unknown.
i7-9900K processor. 
EVGA Supernova 650w G2 PSU.
Two kits of Crucial CT2K16G4DFD824A RAM.  Each kit is 2x16GB. 
Noctua NH-L9x65 cooler.  Stock fan has been replaced with Noctua NF-A9, which has higher airlflow.
Case is an old Lian-Li aluminum mini tower, but nothing from the case is connected to the motherboard.  It's just a frame holding the parts.
 
Guidance would be appreciated.

Cool GTX  - Thanks for the clarification.  On first read I thought you wanted the 24 pin connected to the motherboard but not the 8 pin.  As it turns out, with both disconnected from the motherboard, no, the PSU does not start when I move its onboard switch to 'on.'  This is true with just the 24 pin harness connected to the PSU, and with others connected, as well.  I have to confess I was hoping you were right and that it would be that simple.
 
bcavnaugh - Thanks for the suggestion.  I have registered the board and have opened a ticket asking if it's possible to send me a replacement BIOS chip.
 
MhzManiac - I thought of auto-restart, too.  My first attempts to get it to shut down from the power button before it hangs have failed; I'll try more tomorrow.
 
Given the value of time, if getting the BIOS chip can't be done quickly (or perhaps at all) I'm considering buying an 8th gen i3, putting it on this board, and if it boots, use it to upgrade the BIOS to 1.08 or above, then shelving the i3 until my next build.
 
Thanks to all for your help.  It's appreciated.

EVGA support has let me know that the BIOS chip itself can't be replaced on the Z370 Classified K, but they did offer to upgrade it and return to me at no charge, as they did for Jc.  Given the generally weird POST behavior I'm seeing, and the strong chance that I might have other hardware that's actually defective, I'm uncomfortable waiting a week or more.  I've ordered an 8th gen i5, which I will use to upgrade to current BIOS and then retry the build.  I knew ahead of time that the board might not come out of the box with the BIOS needed for the 9900K, so this is not really a big issue.
 
Thanks to all for your help and suggestions.

An update:  I bought an i3-8300 and was able to POST and upgrade BIOS to 1.14.  So, at this point,  I should be able to put the i9-9900K back in and go on my way. But I still have one issue:

The system powers on and starts to POST as soon as the PSU is turned on.  This is true even with nothing else attached to the motherboard - no front panel, no USB, no video - and with the only connections between the motherboard and the PSU being the 24 pin and the 8 pin for CPU.  (CPU fan is also connected to the motherboard.)   The PSU does not start up when it is disconnected from the motherboard.  PSU is an EVGA Supernova G2 650.
 
Since I haven't installed an OS yet I don't know if doing a shutdown from within an OS will work. 
 
Any ideas?  Thanks to all.
 
 

Glad you got it all figured out and it's working now.
 
Nice computer build! Good luck with it.
 
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