In case you have no web interface access, you can try the following procedure:
1. Turn off/unplug TRB142.
2. Press and hold reset button, at the same time plug the power cable and keep holding reset button for about 5 seconds (mobile signal LED's should start blinking).
3. Download "ADB software" and "rootfs.ubi" file from here: https://kaunas.teltonika.lt:444/f/a9ffe2e9d98446f2aaf3/?dl=1.
4. Install ADB software
5. Place rootfs.ubi file in any easily accessible directory (e.g. in "C:\Test")
6. Open CMD ("Command Prompt" window) with administrator rights
7. Use cd command to navigate to the place where you saved the rootfs.ubi file (Example: cd C:\Test)
8. Then use this command: fastboot flash rootfs_a rootfs.ubi
9. When it completes, use this command: fastboot flash rootfs_b rootfs.ubi
10. When both commands are executed and finished running, unplug power from TRB and plug it again. It should boot up as normal
11. Install intermediate firmware version, which can be downloaded from here:
12. Install desired firmware version to TRB through WebUI. Latest firmware can be downloaded from here: https://wiki.teltonika-networks.com/view/TRB142_Firmware_Downloads.
If this recovery method did not help, you may need to send the device to warranty for repair. The warranty process is described here.