2000 Plymouth Voyager Turns over but no spark

I was driving to work and all of a sudden the engine stopped running completely. It didn't die down slowly, just stopped running. A friend of mine came to assist and tried to diagnose the problem. We checked the fuses (under the hood and under the dash) and found no burned up fuses. We checked for spark at the plugs and found none. We checked for spark in the distributor and found none. We removed the ignition coil (?) and took it into AZ to be tested. It came back okay. My friend thinks that the timing belt has broken. What else do I need to check before going down that road?

Thanks,
Marion