Do you have a good pattern of eggs/larvae/capped brood? Either the queen is being superceeded, or she's already gone with a swarm. They won't make new queens if they have a healthy queen and enough space.
If they were preparing to swarm, destroying the queen cells probably won't stop them. It will just leave you with a queenless hive and no young eggs to be made into a queen when the queen eventually leaves with the swarm.