Solved. I had to reset RYZEN MASTER where I had set it in 'Gaming Mode' to "auto overclock", I think I had to EXCLUDE MEMORY from the auto overclock (involved a convoluted sequence where I had to clear CMOS (button on back of motherboard), then re-enable the XMP Memory Profile for 3600 mhz, then reboot, then restart Ryzen Master, select the Gaming Profile, click "EXCLUDE" on the memory portion, then click RESET, then reboot, and bingo, the 16 cores reappeared. Not exactly a can of corn! Thanks for trying to help me, Martin. Appreciate your time and effort very much.