Unable to Mount External Hard Drive on LL 7.0

[dheo]

Do you use this disk on multiple systems e.g. Windows or older Linux ? Just LL. When I couldn't open it with LL7.0 I opened with an old laptop with Windows.
Is there anything important on the external disk ? Yes
If the contents are important, are they safely backed up somewhere ? I use this disk as a backup

Disk /dev/sdc: 74.51 GiB, 80000000000 bytes, 156250000 sectors
Disk model: A             
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: dos
Disk identifier: 0xac3e155f