Tenant's Right of Possession and Right of Entry by Landlord
The landlord is required to assure that the tenant may have possession of the premises at the beginning of the lease term.
If the landlord fails to provide tenant with possession at the beginning of the term, tenant will not owe any rent until he is able to take possession. If tenant chooses, he may cancel the lease if he so notifies the landlord in writing before he is able to take possession of the premises. The landlord must then return to tenant any money or property given as security deposit, prepaid rent, or other deposit.
In either event, whether tenant terminates the lease or not, he may collect from the landlord any consequential (resulting) damages he actually suffered after he notified the landlord that he was unable to take possession.( However, the tenant must try to minimize his losses. See "Mitigation of Damages".)
Read the Law: Md. Code, Real Prop. § 8-204 
Right of Entry by Landlord and Tenant's Right to Privacy
The tenant has a reasonable right of privacy; that is, the landlord does not have the right to enter the premises at any time and for any reason. If the landlord does this, he may be guilty of trespassing.
However, the landlord has a right of reasonable entry for such purposes as to inspect the premises, make repairs, show the premises to a prospective new tenant, etc. Except in case of emergency, landlords are advised to notify the tenant and reach a mutually acceptable agreement about the specific time of entry.
The balance between tenant's right to privacy and landlord's right of entry can usually be reached by a fair and reasonable agreement between tenant and landlord.
NOTE: IN PRINCE GEORGE'S COUNTY, LANDLORD IS REQUIRED TO GIVE TENANT 24 HOURS' NOTICE BEFORE ENTERING THE PREMISES EXCEPT IN CASES OF EMERGENCY.