Troubleshooing advice, please...

I hope I can get some guidance here. My desktop computer that I built 
several years ago just died on me - as I was watching, it appeared to 
be  going into sleep mode, which it does after some hours of 
inactivity. However, it could not be awakened, it was dead. I 
immediately thought the power supply had gone bad, and in fact, I 
tested it with a multimeter and it was, indeed dead - no voltage 
detectable on any pin. So, I bought a new PS of similar specs. Now, the 
motherboard (ASUS Prime Z270-K) lights up, but there is no other 
activity, no fans going, no display, no disc drives spinning. I can 
only wonder if when the PS blew it took out the mobo or some other 
component.

So, my question is, 'what can/should I do now to confirm that the mobo 
is truly, irretrievably gone?' If I can't, I will proceed toward a new 
build or buy, but if I can revive the existing one, VERY much the 
better. After all, it's tuned to a fair-thee-well and I don't look 
forward to going through months of tweaking to get it to that point 
again.

Aside... A year or so ago I replaced the mechanical boot drive with an 
SSD drive. If THAT had gone bad, would the mobo not still boot with at 
least a display and error message?