one of my doors will not lock, nor will it open from the inside... what do you think needs to be fixed on it

 

Take the door panel off and see if you can find anything out of place. One of the common problems with the door locks is that the little 'door' where the key goes becomes loose and gets stuck inside the lock causing lots of problems. I've had several occasions where my door locks dont' work at all then after going over a few bumps i can slide my key in with ease and lock and unlock.