How can i fix my vauxhall corsa locking system?

PLEASE HELP!

my car doesn't lock when i use the key.
it started off just not letting me lock it from the driver's side and now it won't let me lock it from the passenger's side as well. (as everytime it locks the driver's side doesn't and so the locks automatically unlock again)
even when i push in the lock on the driver's side before i close the door (which then locks all of the doors) as soon as i close the door, all the doors unlock. i have spent up to 15 mins now getting the car to lock, the solution changes each time.

My car is a VAUXHALL CORSA 1.2 1998