Nissan Repair: 1999 Altima timing belt, open valves, valve damage

Question
My son's 1999 Altima stopped running the other day while he was driving. It appears that the timing chain/belt is broken. I haven't taken it apart but when the engine turns over the distributor doesn't turn. Is there much chance of any serious damage to the engine from the break?
Thanks for the help.

Answer
If the chain broke there is possible valve damage from the open valves being struck by the pistons.  Change the chain and then check the compression to be sure.  Oh, you could have a broken roll pin in the distributor and that could be the cause of the distributor not moving.  Lastly, if the cam is broken it could cause the distributor not to move.  If, when you crank the engine, it really turns over fast you probably have a broken chain.  You will hear the difference in how the engine turns over when a chain or belt is broken.