ok so i choose to become a vampire. only.. i can't talk to the Npc Garan marethi, he keeps saying to me ''Mortals arnt allowed to roam free of this castle go speak to lord harkon to fix this at once! ??? i am a Vampire! I have tried to speak with lord harkon again and again! nothing to speak to him about this.. I fi change into vamp form everyone in the castle attacks me! Wtf... Anyone please! advice with some help on how to fix this!. did not spend this cash on the DLC to be stuck and not continue.

Go get cured of your vampirism, there's a quest to do this involving a black soul gem (google it, I forgot the specifics) then try it again. If that fails...well I hope you're a PC user so you can use console commands, otherwise you're screwed.

No, you are not 'screwed'. Go talk to Falion in Morthal, and follow http://www.uesp.net/wiki/Skyrim:Rising_at_Dawn. Then go talk to Harkon and get your vampirism back. Should fix it.