Whether the lease is valid does not depend on whether or not you move in.
You have a signed agreement, along with money paid for the deposit.
Yes, the lease agreement is valid.
I agree with Mr. Russo. However, if there is a clause that signifies an "effective date" in the lease tied to obtaining possession of the premises (moving in, receiving th ekeys, etc) then if there has been no transfer of possession that might help you out. That is pure speculation though, as I have not seen your lease and most leases do not have such a clause.