When a Ext4 filesystem stopped to mount properly enter in a terminal:
dmesg | tail
If the result is: "EXT4-fs (sda1): group descriptors corrupted!"
Check for backup superblocks, replace the x’s with your partition name
sudo mke2fs -n /dev/sda1
"Superblock backups stored on blocks:
32768, 98304, 163840, 229376, 294912, 819200, 884736, 1605632, 2654208"
Restore the superblock from the backup, again replacing the x’s with your partition name, and block_number with the first backup superblock
sudo e2fsck -b block_number /dev/sda1
replace sda1 with the drive it is concerning.