Hi Nik,
This usually happens when you update grub from the wrong OS. .....
And move your boot device from sdc to sda --> swap sata ports.
dep only fiddled around with the fans, nothing else (he said)!
As he has a running system - only from the wrong disk - there's the
foremost simplest approach, reorder the boot-sequence in the BIOS. And
then edit grub.cfg *both* on sda and sdc to have the correct
disk-nomination (UUID, Label....) as startup.
Regards, Peter
.