Should/can I sue?

I sold my car to this guy and we went to my bank to take care of the paper work and then the check came back returned because my bank forgot to have him sign it. Now my buyer is very hard to get a hold of and he is not calling, either me or my bank back to come back and sign the check. What kind of legal action can I take and if theres anything I can do who should I go after my bank or my buyer?