Williams Firepower2 pinball machine problem

[aborup]

I have run all the factory on-board diagnostics without any errors. There are no errors on the CPU diagnostics. All lights, switches, and solenoids seem to work fine. When I power the game on, it always shows "4" in the credits and "0" in the match area. Toggling it off/on - off/on puts it into Game Over status. Nothing seems broken, but when I add credits and push the "start" button, NOTHING HAPPENS. Power is on, lights are on... it's like the button doesn't work (but I tested it and it does).
What are my next steps? Replace all the ROMS?

 

[aborup]

Follow-up - PROBLEM SOLVED!
After reading threads from other forums, I found one that suggested that I assure that there were two balls in the outhole. There were, but the sensor wire that detects them was bent, so the machine did not know that they were there. I fixed the sensor wire and VOILA! I now have an operating pinball game again!