menu button not working

Is it just the buttons on the back, or also the ones on the top, front, and side?

If it’s just the back, it could be just the cable that connects the back buttons to the mainboard that has come loose, or has become faulty. You could try opening up the camera and when removing the back check the ribbon cables, and could even just need to reseat them in the connectors to get them working again.

If it is all the buttons all over the camera, then sadly, it is likely the mainboard that is faulty.