Can a landlord lock a tenant out for not paying rent?

No. A landlord may never lock a tenant out of their apartment. Also, a landlord may not shut off utilities or other services for failure to pay rent or any other reason. Actions such as these by a landlord will give the tenant the right to sue the landlord for committing a self-help eviction. A tenant may be locked out by the Marshall if the landlord wins the Unlawful Detainer Action in court.