Nokia :: N73 - When I Enter The Master Code It Says Code Error

My N73 worked correctly until 3 week ago,suddenly i see when i press button 2, it write 7 ! and continue whit 887734... !then i reset it by code " *#7370# " but problem not solved !i tried 3rd time but the problem was existing yet !Then I opened the keypad and clean it, and restarted again,it worked and all of keys was correct. i set a lock code, and it was working true,until yesterday. Since yesterday, it didn't work , I get my IMEI to a site, and it gives me a ten digit code that calls master code, and said if I enter this code instead of my forgotten code ( I didn't forget it,it didn't work) it will accept by phone. But when I enter the master code it says "code error" too. I tried to hardware reset , but when i hold 3,* & green buttons and turn it on, phone asks me "continue using the phone in offline mode? " (it asks since when i tried to enter deference codes for several times), and i should to answer this and press other keys instead of these 3 buttons, so it didn't work too, I opened it key pad and clean again,but it couldn't help.