Please look for the JPME1 and JPME2 jumpers located on the motherboard next to the chipset heatsink and the SATA/SCU ports. Remove the AC Power, change it from 1-2 position, to 2-3 to disable it. Then update your BIOS. After the update is finished and the system restarted. Remove the AC power and change the jumpers back to 1-2 to re-enable it. When the system comes back up, the IPMI sensors should show again.