How did the sump pump fail? Bad unit or power failure due the hurricane Sandy? If it was due to Sandy I do not think you will be successful in suing your landlord. If a bad unit then contact a local attorney.
DISCLAIMER: David J. McCormick is licensed to practice law in the State of Wisconsin and this answer is being provided for informational purposes only because the laws of your jurisdiction may differ. This answer based on general legal principles and is not intended for the purpose of providing specific legal advice or opinions. Under no circumstances does this answer constitute the establishment of an attorney-client relationship.