Hi dajonx,
Thanks to update.
It's look like a Hardware issue. May iDRAC and Life Cycle Cotroller are in bad state.
I will recommend you the following steps.
1. Reboot the server and reset the iDRAC (While booting
press Cnt + E )
2. Reboot the server press F10 and boot into UEFI mode and
select "Exit and Reboot"
3. Do power re-cycle (Disconnect the power cabel ~30 Min)
4. Make sure there is no external partition is mounted on
your system.
After doing all above four steps perform OS Drivers Pack
update.
Hope this will help you.
Thanks,
Nitin