Cannot access hard drive even though it appears to be there

I am baffled. I have been using linux since the 90s and Ubuntu forever. I am not a computer technical expert but have built several computers and gone through several HDD crashes but not one like this. I have been running 18.04 media server for 14 years. 18.04 LTS was the last time I upgraded it. It also has virtual box and my website on it.

My /etc/fstab file has the usual then:

UUID=84edaaff2c-c293-4a73-9436-93172f5563fd /mnt/84edaaff2c-c293-4a73-9436-93172f5563fd auto nosuid,nodev,nofail,xgvfs-show   0 0

Until yesterday, this HDD accessed in filemanager by /mnt/84edaaff2c-c293-4a73-9436-93172f5563fd held 30 years of my favorite songs and bunches of old movies,books etc. It is a 2tb seagate.

Today, in my filemanager I see /mnt/84edaaff2c-c293-4a73-9436-93172f5563fd but it is empty. No files at all.

Blkid lists all the other UUIDs in my /etc/fstab but no sign of 84edaaff2c-c293-4a73-9436-93172f5563fd

fdisk -l lists my 500gb /home and my other hard drive 3.7TiB storage drive but no sign of the one I am looking for and gparted didn't find it either.

Yet there it sits in my filemanager under /mnt/84edaaff2c-c293-4a73-9436-93172f5563fd, properties 4.5GB and no files. This morning it was owned by root, which I changed to me and I can write and access file in /mnt/84edaaff2c-c293-4a73-9436-93172f5563fd.

Testdrive - no sign of it ... the /dev/sda and /dev/sdb are there but no sign of the missing 2TB drive? I tried the alternate superblock address - no joy.

I took the hard drive out and plugged it into my Ubuntu Desktop via a USB Sata adapter. There was no sign of it on the Ubuntu Desktop.

I put it back in the server with a new SATA cable and into a different plugin site on the mother board - same as above.

I do not understand how the UUID can show up in my filemanager, be empty and not show up anywhere else so I can try to recover all my lost files.

I would appreciate any thoughts on this one, I hope I am missing something really obvious, it would be nice to get my tunes back.

Thank you in advance Steve

Everything in your description indicates that the hard drive in question is defective and no longer works.

/mnt/84edaaff2c-c293-4a73-9436-93172f5563fd is just the mount point in your filesystem where the drive would be mounted if it was still functional. If the drive is unmounted, or doesn't get mounted in the first place because it no longer works, the mount point remains there as an empty directory.

The fact that the disk didn't show up when you connected it to a different computer via a USB SATA adapter is a very strong indication that it is defective. In the best of worlds you would have a backup of any files you really care for, and now would be the time to restore them to a new disk from that backup. If you do not have a backup and those files are really precious to you then you might turn to a data recovery service to try and rescue some or all of the data from the defective disk. That option is not cheap, though.