If your display doesn't show anything, it's probably that the connector got loose.
Worry not, it's super easy to fix :)
It's on the back of the Gamebuino, to the right of the battery. The cables comes from underneath the battery.
1- Pull on the black thing to get it loose
2- Put the orange ribbon cable back in the connector as much as you can
3- Push back the black thing to lock the ribbon cable in place