Changing locks is not legal but you can be evicted for non payment of rent. You have the right to pay in full and catch your account up to even (with interest) to honor the lease. Beyond that you have the right to service of process on the eviction case to satisfy Fifth and Fourteenth Amendment due process.
Your landlord cannot resort to self help. If the locks are hanged you can call a locksmith to get in. If that does it work, hire a lawyer and get into court ASAP.