doors not unlocking

My rear drivers door wont unlock with either the key fob or manually lifting it up. The door has to be open to remove the door panel. I dont want to spend the big bucks to fix it if I can fix it myself.

I will be a brief as possible. This is driving me CRAZY! I have the following problems, and I am not sure when this all started as this is a relative's vehicle. 1. right front & both rear doors will not unlock with remote key. (does work with switch on both front doors) 2.express window open...