Think the board is burned but have you ever heard of this?

[LarryM]

Xloader - instructions

How to use Xloader to load a new version of grbl into the Arduino/X-controller. The left screenshot shows the window that Xloader displays when it starts. Enter the file path or browse to the .hex file that you would like to load into the Arduino/X-controller. Select the device type you are going to load into (Uno/ATmega328 for the Arduino/X-controller). Select the COM port where your Arduino/X-controller is attached. The baud rate should be 115200. Press the “Upload” button. When the .he…