You have a bad door lock timer (DLT). Applies to 92-94 Maximas. It causes the power door locks to stop working periodically and then completely. I had the same problem and fixed it this past weekend.
Where is the DLT? Take apart the under panel under the steering column, to be more specific the big piece that surrounds the fuse cover lid. Once you remove all the bolts it will come down. Don't forget to take off the hidden screw on the left side (left side of the fuse panel).
You don't have to remove the defogger switch only the panel. Once its out look at the right side of the steering column (would be above your right knee when seated) and you will see a grey box and when you remove it, it should have a sticker that says "door lock timer".
How to Fix It? The DLT has 8 capacitors (cylinderical radial) as follows:
25v 100uf (2)
25v 10uf (4)
50v 10uf
50v 2.2uf
Usually, it is the capacitors that dryout over time and DLT stops working. If this is the case, you can replace the capacitors. I would recommend starting with the 25v 100uf first. I replaced these with 35v 100uf (radio shack 272-1028). I only had to replace the first two because after I replaced the second one and installed it, the door locks started working. The capacitors do have polarity (positive/negative) and should be installed appropriately. The negative is almost always indicated on the capacitor and on the circuit board.
You will need: Soldering iron Solder Capacitors A steady hand
If you can find someone to do it in your area, thats great. However, there is no guarantee that this will fix it. I did work for me. Please you the above information at your own risk.