The main CPU boards are very easily damaged by leaking batteries. Have you checked the area around the batteries if there is any signs of corrosion? If so this is most likely the cause of all your problems. I have a similar problem with my Bally Star trek. Sometimes it works and sometimes it doesn't. A simple jiggle of the wiring or a slight push on one of the IC chips will often bring it back.

Even very minor battery damage can cause problems with connectors and chip sockets. The solution is to remove the battery back and relocate it to a safer area. Clean all possible effected areas, replace any questionable components, replace chip sockets. There are lot's of online guides regarding what needs to be done to repair battery leakage damage.

I just got a Data East Back to the Future that would give me a sound call out and GI lights at start up. But nothing else worked. CPU board had some pretty bad battery leakage damage. My solution was to purchase a new replacement board. Installed it and everything works!

Good Luck!!