I have been having the same exact problem with my 1994 Nissan pickup as well. The starter began acting up a few weeks ago, where it would not crank when I'd try the key. I replaced the starter and it didn't do a single thing to fix the problem (although the starter was the origonal on the truck with 160k miles). I started unplugging and plugging the relays under the hood to make sure they were all seated properly, and still nothing when I tried to start it. I finally opened the fuse panel under the driver side, ran my thumb over the bank of fuses just to feel if any were loose. I then tried starting the truck again, and it fired right up. I figured that was the problem, and it was starting perfectly for a couple days. Now it's back to the same issue as before; won't start. My guess is possibly either a bad relay in the fuse box (i checked all the fuses), or else a loose wire perhaps? I'm also wondering if possibly it could be the ignition switch on the column..