During the C220 M4S POST (Power On Self Test) the system may hang during power on.
Bios version encountered this on was: C220M126.96.36.199b.0.1201161639
BMC/CIMC Firmware was on 3.0.(1)c
POST hung on this screen: Configuring platform hardware screen.
Subsequent reboots have no impact. and no noticeable errors or alarms present.
The trick is here is to activate the backup BIOS and reboot the nodes.
Once you activate the bios you will need to fully power off the node and power back on in order for the BIOS change to complete.
On power on the server should then go through its normal boot sequence
I would suggest mounted the Cisco UCS Host upgrade Utility and upgrade/downgrade to the required firmware