The major problem on android phones the users facing is Pattern lock problem the users forget their pattern lock code after entering the incorrect code its shows to enter the user name and password to unlock your account but u cant unlock in that. Just remove your back door and remove your battery and re insert the battery and press the volume up button + back key + power on button wait for 10 to 15 seconds it shows the boot loader menu just select the WIPE CACHE PARTITION  by using the volume button and to select using power on button then select REBOOT.. Your problem is solved..