I found the problem but cannot explain it. POST code error A2 is supposed to point to HDD issue. New I7 3770 gave same problem on Stinger and Gigabyte mobo's. On a whim I changed the monitor cable. I had HDMI to HDMI cable originally and changed to HDMI-DVI cable(HDMI to mobo and DVI to monitor). Voila' both mobo's POST'ed. Both cables worked on other computers. I don't know if HDMI input on monitor is bad and I can't explain why that would prevent booting. Either way I'm glad it is fixed.
Hope this helps others with problems.
Mobo...EVGA Z390 Dark
CPU...I9 9900K .
GPU...EVGA GTX 2080 Ti .
RAM...Corsair Vengeance RGB PRO 32 GB 3200MHz
SSD...Samsung V-NAND SSD 970 EVO NVMe M.2 2x2TB
PSU...Silverstone Strider 1500W
Case...CoolerMaster HAF
CPU waterblock...
EVGA 240mm CLC
OS...Windows 10 Professional 64bit
Headphones...Beyerdynamic DT770 Pro
Monitor...BenQ 27" 120Hz X2
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