There is little concise information to pinpoint the specific issue. You did not indicate how both drives are "not reachable".
In general, Ubuntu can work with many file systems. When a file system is mounted, its content will be displayed in the File manager.
Partitions on external drives, e.g. drives connected through USB, are automatically mounted.
Partitions on internal hard drives are not automatically mounted. They can be manually mounted by the user by clicking their icon in the left bar of the file manager.
The permissions by which file systems are mounted differs between file systems:
Partitions formatted in fat32 or vfat, i.e., file systems not supporting file permissions, are by default mounted with full permissions for the current user.
Partitions formatted with the default file system of a windows installation, ntfs, also are mounted by default with full permissions provided the file system is clean, i.e., provided the file system previously was correctly closed and is consistent. If the latter is not the case, Ubuntu will mount such file system read only.
Partitions formatted with a file system that supports linux permissions will by default be mounted as owned by the administrator. For the user to be able to access the file system, the administrator first must change ownerschip of the entire partition, or of selected directories on that partition, to the user. Such changes in permission settings are remembered.
Since you can load Ubuntu, you are at least seeing the data on the system partition on the SSD on which you installed Ubuntu. You can see the contents of the top level directory, which is symbolized by a simple /. In the file manager, click "Other locations", then under "This computer" you should see the system drive labeled "Computer" under Ubuntu.
Other partitions and drives are not visible there. They should show up in the left bar. Once a partition of a different drive is mounted, it becomes part of the directory tree. Under Ubuntu, external drives are mounted under directories created under /media//.
If a partition does not mount, then indeed there might be strong damage to the partitioning or file system. In a first step, you could, in the file manager, right-click the drive icon then select "Properties" to see information about the drive, including the file system. A more thorough way to debug is to mount the drive using terminal commands. Feedback and error messages in the terminal may hint to what is wrong.
To mount a drive manually
Make sure it is not mounted - right-click the icon on the drive and see if you can select "unmount".
Open the terminal
Issue the command lsblk. It shows all your devices, and eventually where they are mounted. In Ubuntu, there are a lot of loop devices. Ignore these. Your connected drives will likely be listed at the end of the list. The listing is in the format
NAME MAJ:MIN RM SIZE RO TYPE MOUNTPOINTS
sda 8:0 0 931.5G 0 disk
└─sda1 8:1 0 931.5G 0 part /media/1000/Files
nvme0n1 259:0 0 476.9G 0 disk
├─nvme0n1p1 259:1 0 600M 0 part /boot/efi
├─nvme0n1p2 259:2 0 1G 0 part /boot
└─nvme0n1p3 259:3 0 475.4G 0 part /home
/
You see two disks here, sda and nvme0n1. The latter is my SSD disk, the former a connected SSD USB drive.
You see a single partition on the sda drive, sda1. All these devices, i.e. disks (e.g. sda) and partitions (e.g. sda1) can be accessed by their device name, i.e. /dev/sda and /dev/sda1 respectively.
This is enough information to attempt a mount on the terminal. We specify the partition to mount, and the directory where it needs to be mounted:
sudo mount /dev/sda1 /mnt
If successful, there is no output. You should be able to see the contents of the partition in the directory /mnt, i.e., the directory mnt residing in the root file system /.
If not successful, warning and error messages may hint to the cause of the problem.
