There's a few components that can go bad. In reverse order, you've got the dynamic buttons, going to the ribbon cable, which goes to that little board mounted in the door. From there you've got the HDMI cable running its way to a board mounted on the back of the cabinet. That one is actually two boards, one mounted on top of the other. That board has the HDMI, a USB and a 4 pin power connector. Your buttons look like they don't have power. If the USB cable were disconnected, you'd get a USB Timeout error. If the HDMI disconnects, you'd get the firmware version number, the button position, and a letter. Can't remember if that shows up while the hdmi is unplugged or if it shows up as soon as you plug it in.
Anyway, check your 4 pin power connector first, then the HDMI. That cable is a common failure point for my MLD games. It's nothing special, just a regular HDMI.