The system was installed with Windows-8.1.
A recent upgrade to Win-10 causes it to freeze at boot, right when the spinning circle appears. The spinning circle actually spins for 1 second.
Only option is to cold boot and hope it doesn't happen again, which usually it doesn't do; on second cold boot, it boots fine and everything seems fine.
The freeze always happens if a warm reboot is performed, by going to Start Menu and pressing "Reboot/Restart".
So, basically, on second cold boot, it always starts up fine.
The motherboard is a Supermicro X9SRL-F.