Mellon, thanks for your input. Exchanged the motherboard today. MicroCenter let me do so after about 60 days, so big thumbs up for that. Good Lord, so glad I didn't mail order this stuff, I'd be here until the sun swallowed the earth.
I've got everything out of the case, started completely at square one. Only thing hooked up is the PSU, CPU & fan, 1 stick of RAM, 1 case fan. About two hours ago they all worked. I ate some dinner, came back, now nothing works. I'm at my wit's end...
Maybe it is the freaking PSU after all. Unfortunately, don't have a spare to test, or a voltage meters, etc.