Before buying any new boards, I'd be trying to get the existing one working again.

When did the existing board stop working? I.e. Just randomly after being powered on? While running a job? After changing a setting?

Does the board still show as being connected to the computer? I.e. listed as a COM port in windows device manager?

I've got no experience with GRBL, but I'd suggest trying to send some commands via a terminal to the board to see if it responds. For a terminal, it's probably easiest to download the Arduino software, as it includes a terminal, and you'll need the software anyway if you do need to reprogram anything.
If there is no response, I'd then be trying to re-flash GRBL to the board, as something could of caused it to become corrupt, and re-flashing it may get things working again.