On the CPU board, there are three LEDs - what are they doing ?
One will flash constantly when the game boots. If not, then it can be a number of things.
An update, I had a closer look and there are 3 and they stay on constantly (no flashing).
Thanks!
Sounds like you are getting +5V.
Try reseating the ASIC chip (the big square IC) - just give it a push in the four corners. Reseat the ROM, CPU and RAM.
Hopefully the board has no acid damage from leaky batteries ?