Receiving an error sometimes when booting "CPU Fan Error, Press F1 to
Continue". All fans are confirmed working.

CPU temperature when booting to BIOS upon boot is about 42C/107F and
climbing rapidly.

When booting into Windows, temperature reduces to about a steady 38C/100F.

Cool n' quiet is disabled.

Thanks in advance for any help.

Do you have Q-Fan enabled? This will throttle fan speeds according to
CPU temperature in order to quiet down the system. (It operates
independently from Cool'n'Quiet.) In my experience, it doesn't work
well, so I just turned it off.

This particular problem seems to be caused by the fact that when the
system is powered up cold, the CPU hasn't warmed up enough to require
the fan to come on when the POST checks CPU fan speed. So it complains
about a fan failure.