My Prizm's engine died going up a hill on 1994 Geo Prizm

My husband was on his way to work the other day, in his trusty little 1994 Geo Prizm, when all of the sudden, the engine dies and the car will not start. He managed to get it towed home but it still will not start. The starter engages, but the engine will not turn over. Any ideas as to what could be the problem? It has close to 240k miles.

Asked by for the 1994 Geo Prizm
So many things can cause the engine not to start or stop running it is hard to guess at a cause without being able to do some diagnostic tests. An engine needs fuel, spark and mechanical integrity to run. Fuel pressure and volume is easy to check (even "opening" a fuel line while someone cranks the engine over will verify the presence of fuel but won't verify pressure). Ignition spark is easy to verify, and after that plugging in a scan tool to the 16 pin diagnostic socket under the dash can verify the operation of a lots of key engine sensors without having to do intrusive testing at each sensor. Many sensors on the engine are shared by both the ignition and fuel system, failure of any of these may cause an engine to stop running. An engine has to be able to develop compression and the components must stay in synchronization with each other for the engine to operate properly. Most engines keep the components in synchronization with each other using a timing chain or timing belt. It is unusual for a timing chain to fail ( a timing chain that is about to fail usually has associated engine noise long before it fails), a timing belt on the other hand can fail at any time and that is why they are replaced at regular maintenance intervals.
Thank you. We have narrowed it down to the timing belt. A few of the treads on the belt have come off. One more question though, if the timing belt does this, does it cause any damage to the engine?