Sounds like your starter needs to be replaced.

Replace key switch.

    Greetings and salutations...

    If, when you turn the key to hit the starter, you hear
a click...but nothing happens...it is probably a bad starter.
If you hear NOTHING, then, it is possibly the ignition switch
or a safety relay.
    FWIW, I am going through this with a 1992 Sentra.   It
has been flaky for a bit...first off, a year or so ago, had the same
problem.  Got a click...got no turn on the starter.  I tried swapping
the starter out, and, found that the alternator had gone bad TOO.  It
would put out voltage, but, not enough current to keep the battery
fully charged.  So...swapped that out, and, the battery (as it was not
keeping a good charge either, any longer.   After all this...things
worked ok.  Well, over the past couple of months, it has gotten worse
again.   Of course, my housemate, whose car it is, would have to
turn the ignition switch 40+ times to get it started.  When I would
check it, it would start on the second or third try (at most).
Needless to say, this caused a bit of ire and frustration *smile*.
    Well, as the starter was so new, I wandered off on a path
of thinking it was the ignition switch...so put a new one in at
$55.  At least Nissan was bright enough to design it so the lock
cylinder is separate from the electricals, and, so it was a fairly
painless job.  It fired up first shot for about a dozen starts...
then..when dead.  I had seen a posting about the positive cable
from the battery to starter dying, so was thinking THAT might be
the problem.
    Managed to get it started once more, and, took it to her
usual mechanic (I am short on time just now...so it was a good
thing).  He called later that afternoon to say that it was, indeed,
the starter - in spite of it being so new.   We have not gotten
the car back yet, as he has a slight oil leak to track down,
but, I will be interested to see if it works after he has put
a new starter in.
    By the by...the replacement starter was an aftermarket
item...I begin to think that the folks that post strong
suggestions to only use genuine Nissan starters are right.
    Regards
    Dave Mundt