System will not boot after 8.1 upgrade

[Veles]

Everything worked flawlessly for 2 years now until the 8.0.3 to 8.1 upgrade. Now on boot, I get the following screen. Any idea what might be the cause and a possible fix?

 

[leesteken]

This is a motherboard BIOS message. It's unlikely that a normal upgrade form 8.0 to 8.1 damaged the boot partition. Maybe the CMOS was cleared or the battery ran out? Have you tried changing the boot drive in the BIOS or select the correct boot drive manually (procedure depends on the motherboard/BIOS)?

 

[Veles]

Ok after a BIOS check, it seems my WD NVMe is not recognized anymore (only my Samsung NVMe). I replugged the NVMe and it showed up again in the BIOS and the system booted normally. Very weird...I need to check the drive or the slot.