Could a valve cover gasket be the reason that my 1989 probe LX is not turning over?

Put it in neutral and put a wrench on the harmonic balancer bolt. Will it turn over by hand. Unless the gasket is wrapped around the camshaft I seriously doubt that is your problem.
I worked on a VW where a rag was used to plug the oil fill hole. It got caught and wrapped around the camshaft stalling the engine.