If you like we can try to find the cause of the failure.
- extract KoboRoot.tgz from the uploaded archive and install it
- navigate to the usb menu and select: "enable usb log.sh"
- This is not expected to work any better than "enable usb.sh" does. So you will have to restart the device afterwards. The only difference is that it creates a log file.
- When the device is powered on again, copy the log file to the user partition by selecting: tools > ksm diverse.msh > copy KSM logs to user.sh
- You should now find the log file in .adds/kbmenu_user/log