help fire under hood when boosting off and want run

I put a new alternator and new battery on it. It ran for 2 days and then would not start up. Tried to boost it off and a fire started. Any help telling me what I can do to get it running? What kind of problems am I having? Could a new relay help? Any help.... PLEASE!!!!!!!!!
Thanks Roxxi
email me with any answers
roxxiwright@alltel.net