Why won't my 1992 subaru impreza start?

The problem began when all of a sudden while driving on the freeway my car stopped. I tried starting it many times without any luck and had to push it. When a mechanic came to check it he found that the time chain pulley was broken so he replaced it and the time chain as well. Still it won't start. Someone told me that with so many attempts to start it I might have bent the head valves so another mechanic checked thenm and they seem to be o.k.
What else can be the problem?