My dog fights with dogs and trys to bite some people and he used to never be this way?

My dog Shorty was a friendly dog with everybody but here lately hes got out of control. I have to lock him up in my room because when hes not he latches on to other animals he knows. I have to watch him around people because he trys to bite some people. I need to know what could be making him this way. What can i do to stop his behavior?