Nightmare landlord please help

I moved into a place that ended up flooding from roof leaking became a fire hazard as well as a health hazard due to mold, as I was moving out landlord tells me I can go to the other apt complex and see about moving in to an apt there, i decide to move into new apt complex and landlord said my deposit would carry over, 3 yrs later I move out of 2nd place due to registered sex offender living next door which I found on national database I confronted landlord on why he couldnt at least make other tenants aware, he stated it was special circumstances, I vacate the 2nd apt complex and 2 monthes later I get a bill in the mail for 1281.00 owed to the last place I lived, when i called the collection agency it came from they didnt really no any details on it so I wrote a letter stating I wanted an itemized bill stating what I owed for and also where did my deposit go, when I get a response it made no sense and didnt ever get an answer as to where my deposit went, I admitted I owed for 2 interior doors and that was all, then when I moved into the third place the landlord did a background check on me and the 2nd apt complex that said I owed all this money slandered me, lied and said I was consistantly late on my rent, which I have all the duplicates from my check book which I was late on 2 rent payments in 3 yrs, if I was such a bad renter why would he let me reside there that long?? anyways the landlord has since ruined my credit by turning this debt into a collection agency and now I feel like I am made out to be some horrible renter when I was most definatly not, do you have any advice as to what I can do legally to this jerk ?????  should I even bother trying to take him to court or contact the big credit reporting places and make them aware ?? I am sooo mad that this guy is getting away with this help help help ;o)