So, to be clear;
you cannot pull on the rope, it doesn't unwind and it doesn't turn over the engine to start?
So, remove that spark plug and see if you can now pull the rope and turn over the engine.
if so, pull that rope a couple of times with a clean rag over the spark plug hole.
if it has some serious oil stains now you might have had too much oil in it.
if you see gas stains you had an issue with your carb.
Anyways, reinstall the spark plug, and try again.
If you STILL cannot turn over the engine, remove the shroud,
check the flywheel for debris that could lock it in place.. also
make sure the magneto doesn't interfere with the flywheel.
you see a small gap only and the magneto cannot be moved with just your hands, then leave it as is and call it good.
try to turn the flywheel by hand slowly (CCW at least one rotation, then Clockwise )
listen for odd sounds
..oh spark plug still removed that is.
Still nothing?
that engine is seized for good and you need to repair it
(since it's a predator it'd be cheaper to replace really I guess)
but no need to not crack it open and see what's wrong imho.
if you found something locking the flywheel, good.. removed and retried it should start

else, tell us what happened. (have you heard something, did it turn...?)
'sid