Hi Widget can't give you a definite answer but is it a bar blade? If so, I don't like the sound of it.
When you say you hit something hard, was it a clump of weeds/grass, was it a tree root our was it something hard like a fixed concrete structure like a step or other hard thing with no give?
Not restarting after stalling it instantly hitting something hard sounds like damage has occurred to some part of the engine structure itself.
