I believe you have the old unlocked bootloader.
Possible you didnt upgrade ?

Try to download https://github.com/djselbeck/jollare...net-initrd.img

and - as root - issue

fastboot -i 0x2931 boot boot-telnet-initrd.img

from where you downloaded boot-telnet-initrd.img

You might need to apt-get install fastboot

Output should be either

1. device boots that image with no errors
In this case, you can get telnet access (see https://wiki.merproject.org/wiki/Sailfish/Backup_Device) and create backups - which will be useless, as your device wont boot. Possibly you can get a copy of all 28 partitions, or at least the root file system to restore this way. However, it is 16GB of data

2. device tells you 'not allowed' in whicg case, you do have the newly locked bootloader. If USB net doesnt work, afraid we are ATM in the situation that you will need to return to service.

So, what does fastboot -i 0x2931 boot boot-telnet-initrd.img tell ?