there are a few possible causes. will list them from most likely to least likely
1- the board is dead ( could be fixable but chances are slim)
solutions :
this could be a hex related issue, can be fixed using this great guide >
https://bitcointalk.org/index.php?topic=5032987.02- a falling PSU
solution : try a different PSU
regarding the error message you get upon flashing the firmware, looks like the firmware is bad, try using a different one, also make sure you using the T9+ and not just T9 firmware, also a hard reset could solve your issue.
* posting the kernel log will help troubleshoot your problem