Bad Boss

I was let go from a job after 5 years wuth no explaination from a very verbal and mentally abusive boss. He would not even provide me with a legit reason for termination. Since then he has done everything he can to prevent me from getting another job due to i beleive giving..bad references. I cant really prove it though since employers do not divuldge this info. What can I do. I was an excellent IS Manager who needs to gt back to work.