Seems like the partition table itself is broken. None of these is able to read if from external system?
fdisk -l /dev/sda
parted /dev/sda print
Kernel logs could give a hint:
dmesg -l 0,1,2,3
But when it’s physically dying, not much which can be done and probably not worth to waste much time, i.e. I agree best is, if it still boots, to rescue as much as possible as fast as possible and setup a fresh system.