I've got the same problem. I used an Arduino to send data to the seven segment display board, via the output pin 8 to the Rx input on the shield. This worked fine. Then I used an Arduino Pro mini board, but instead of connecting an output pin, I connected the Pro mini Tx output to the shield Rx input (dumb !)
I think what happened is that when I sent the program to the Pro mini board, it also sent it on to the shield, so rendering its firmware useless. Now it only shows 0000, even when correctly reconnected to the Uno board.
So now I'm trying to download and compile the firmware routines, so that I can re-program the shield. Trouble is, the only SevSeg library that I've found doesn't have exactly the same methods as are called up in the firmware routine. For instance, it has a method called "Brilliance", whereas the firmware calls a method called "SetBrilliance".
IF I ever sort this out, and IF I ever manage to reload the firmware, I'll certainly let you know.
In the meantime, if anyone can shed any light on exactly how to rebuild the firmware on the shield, I'd be grateful for your help.