I'm not entirely clear on your question. If you signed a lease, but can't move in because a prior tenant has not vacated the premises, your lease should address this situation. If the landlord cannot deliver the premises, your lease should include a provision that addresses your responsbility. If you signe dand moved in, who's the tenant that won't leave? You should not have to pay rent for a place that is not habitable. I suggest you consult with a local attorney.
This should not be construed as formal legal advice or the offer of the formation of an attorney/client relationship. There is no substitute for taking the time to consult directly with an attorney regarding your specific legal needs and issues.
I agree with the other attorney. This question is not clear. It appears that you are paying for space that is not habitable, because of repairs and another (possibly former) tenant who is still living there. These items are all addressed in your lease. I would recommend consulting with an attorney.