With the power off-
remove and reattach the ribbon cable from both the display glass itself and the driver board ends. (All you are doing here is "cleaning" the connection pins and trying to improve the connection).
Power back on - any change?
If not - power off again - your goal is to physically switch the player 3 & 4 displays. You may be able to do this by simply switching the cables (probably not), so you'll need to unhook the cables - pop the displays out and switch them to the other location. Hook the ribbon cables back up and power back on.
If your player 3 display is indeed "dead"....and since you just moved it to the player 4 display....then player 4 should now be "dead". If indeed it is - that's a pretty good indication the score display itself is bad.
If not - and the glass works when you move it to the new location - you've proven the glass is good and then we'll have to start something else. Let me know, good luck.