1993 Maxima Reverse Gear does not engage

My Maxima made a loud noise one day while driving during gear change. Then after I parked it, it would not go into reverse. Right now, it shifts from 1st to third, and overdrive does not work. Could this be an electronic problem even though the check engine light is not on? Will I find any fault codes in the electronic module even though the engine light is not on? I never had any problems with the transmission before, the fluid level is fine. The only thing I can think of is a couple of months ago, I had the CV axles changed, and while the mechanic was working it, the transmission fluid starting pouring out. They filled it back up, and I've been driving ever since. Any ideas?