This would be easy enough to check, just have someone see if the serpentine belt is spinning when the starter runs.Could also be a broken timing belt - no engine compression for the starter to turn over. How many miles, and when was the timing belt last replaced?
I don't believe this is the case though because with a broken timing belt at least one cylinder is likely to have some sort of compression and you would probably be smacking valves with the pistons (if the gas motors are interference, I believe they are)
I vote for the starter too. It's spinning but not popping out like it should.