On the driver side door, the small plastic locking lever which is located within the door handle, broke. I could see its spring had come loose. I was able to bend the spring-end a little, enough to make it continue working.
1992 Nissan Sentra XE   GA16DE    Engine Code "E"
Next, the door began hanging a little when opening. I thought the door striker needed adjustment. I also thought it would be a good time to remove the door panel and determine how to replace the inside handle, if needed. I'm thankful I removed that panel.

Why? Because I soon found that the several screws which hold the door panel in place cannot be accessed when the door is closed. So I removed the panel, THEN I closed the door. That was the last time the door would be opened for four days! Why?

Once I closed the door, it would not open again; not from the inside and not from the outside, even when using the key.

With the door panel removed, I could see the locking rods were connected to the lock actuator and I could move them with my
hand but moving them had no effect.
For the next four days I
tried every trick I could devise to get the door unlocked but nothing worked.

I searched the Web for guidance and I found that many people
with various makes and models had the same problem but I 
found no instructions to solve my problem. I was reminded that
if I hadn't had the door panel off before the door froze in locked
position, I would have had to cut holes in the panel in order to
see the mechanism inside.

On the fifth day, after much fumbling with the locked door, I lowered the window, leaned out and inserted the key, turned it clockwise (toward the rear) and simultaneously I reached down and pulled the inside lock rod upward and low and behold, the door opened as if by magic!!

After finally getting the door open I decided to replace the handle.
The only one I could find was from a dealer who said he could
order it and it would take a week to arrive. The cost for that little
plastic handle would be $40.00! I almost dropped my dentures!

I decided that I could fix the handle myself and I did.