Unable to unauthorize My computer

downloaded the New version digital editions 4.5.2 to my computer win 7. The old version was removed autmatically. Now I tried to borrow Brooks from the library it says "check activation". Got the tip typ unauthorize My computer and then authorize it again. Well I'm totalt unable to unauthorize it.. It says it the wrong password or whatever...comeback back later...I tried that too. I`ve changed the password twice I think..doesnt work at all

anyone got an idea what to do????