Please help, Old Cat and Others - About the house we just closed

We live in Maryland and bought a 44 years old single house recently. The closing date is this Dec. 1 and the house was rent back to the seller till 11th of Dec. Today morning we just took the final walk through and found severe leak in the basement (there was a big rain yesterday night). We have several questions and would like to hear your opinions or suggestions:
1. Do we still have chance to withdraw the house?
2. If we have to keep the house, what could be the best way to resolve the problem?
3. In the worst situation, if the seller refuse to do anything because they think the leak happen after the settlement, do we have a case to bring in court?
Thanks a lot!
Sorry I could not type Chinese on my machine, but can read in Chinese.