Could you try to cogin to your device using an SSH client. It seems that one of your device's internal files got corrupted.
For SSH access, please download PuTTy client, use root as username and your router's password. You can also find instructions here. Next, I would like you to execute the following command and upload a screenshot with its output.
- hexdump -C /dev/mtdblock1
If there is no human readable data, such as a serial number, or MAC address, I would need you to send a serial number of the device to me and we would need to arrange a remote via AnyDesk to restore it.