The supplier concluded it was a fluke, and the motherboard was dead on arrival (DOA) so sent me a second SuperMicro P4DC6+ motherboard. After switching boards, checking all jumpers, reconnecting hardware, etc. I started it up. The same thing happens!
I know the keyboard I was using is good, but I replaced it with a new spare; same result. I've messed with the keyboard wakeup (both PS/2 and USB) jumper settings, but the result is always the same. The SuperMicro logo is displayed on the first BIOS screen, the prompt to press DEL to enter setup or TAB to display POST messages appearing below...pressing DEL at this point multiple times, or holding it steady, does not take me into the BIOS setup program. It only moves to the second screen, displaying a text report of POST progress...reporting on the main CPU, the memory is okay, the master and slave drives, the fact that the CPUs have been changed:
CMOS checksum error - Defaults loaded
Warning! CPU has been changed
Please re-enter CPU settings in the CMOS setup and remember to save before quit!
Then some blank space, and the prompt at the bottom of the screen:
Press F1 to continue, DEL to enter SETUP
...and pressing either F1 or DEL produces no response. I cannot get into SETUP!
I will appreciate helpful clues to debug this issue!