drivers door looking issue
 

hello i am new and need urgently help.
i have a Merc C-Class, 2003.
i am not able to lock the divers side door mechanically and can only lock manually, however all the other doors are not affected.
i do not know if anything can be done by myself, but i am no use in repairing anything anyway. i wonder if i need to buy any new parts or what actually is wrong with it.

would anyone please help me out?????

sharmili