This afternoon my USB to SATA Adapter of my external HDD died. My controller died on the job.

I bought a new Adapter and hoped it will work with it.

the hard drive was recognised again but when I started the hard disc, I got the error message:

Unmountable: Unsupported partition layout

I tried the command: gdisk /dev/sda and got the following feedback:

  MBR: MBR only
  BSD: not present
  APM: not present
  GPT: not present

***************************************************************
Found invalid GPT and valid MBR; converting MBR to GPT format
in memory. THIS OPERATION IS POTENTIALLY DESTRUCTIVE! Exit by
typing 'q' if you don't want to convert your MBR partitions
to GPT format!
***************************************************************

Warning! Secondary partition table overlaps the last partition by
32 blocks!
Try reducing the partition table size by 128 entries.
(Use the 's' item on the experts' menu.)

Command (? for help): 
 

I don´t really know, what i have to do at this point

Can someone help me or is my hdd still dead?

Not all USB bridges are the same, some detected the disk with a different capacity, and that will cause issues, see if the disk mounts with UD, but best bet would be to try and find an identical bridge to the one that broke, and then backup the disk and stop using USB.

5 hours ago, JorgeB said:

Not all USB bridges are the same, some detected the disk with a different capacity, and that will cause issues, see if the disk mounts with UD, but best bet would be to try and find an identical bridge to the one that broke, and then backup the disk and stop using USB.

Thanks for your information. Is that typical for seagate bridges?

 

Typical for a lot of USB bridges, one of the reasons they are not recommended.