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 .