I'm angry!!!!!

hi i'm rox...I went to write my password at the msn massenger but he's telling me that the msn is in two place that the msn is online in another place not only i'm using it ...what am I gonna do...and when i come online the other user will sing me out so I can't change any settings...and i'm really fiurous about it...If I catch the fucker he'll be dead,can you help me out pls...i beg you???