This is the preferred method for "unbricking" a box. You will need a USB Male-to-Male cable to connect the box to your PC.
This is the most comprehensive archive. Search for "TX9 Pro" to find various versions, including the stock Android 7.1 Marshmallow or newer 9.0 builds.
Once you have located a link and downloaded the .img file, you generally have two ways to flash it:
