Plz help with yahoo Inbox?

hi i was using my another yahoo id nicely and at once it said ur session has been expired and log in again . i did that but its not signing in .. its saying that wrong id or paswd. i m frustrted of it .. i dont know what happend . i want that id bac. all my important university emails and contacts r there. plz let me know .......... how should i get it back .. nd wts rong with it ... is there any one who is having same problem