Timing belt
2 Answers
If the engine is turning over and the timing belt is not turning, that could mean that the Teeth on the Belt, right at/around the crank pulley have been stripped off. If the belt is old, or has had oil leaking on it will get week and when you try to start it could loose some teeth (ribs on the inner part pf the belt). If the ribs get worn/missing the engine will rotate but WILL NOT move the belt with it.
Belt tentioner might be loose or broken. Regardless, u need to take it apart and re-time it. Check camshaft for damage before u re assamble it