2000 Checy S-10 won't start sometimes

I have a 2000 chevy s-10 with 85K miles on it. Occasionally it has pulled this little trick since I bought it new. It use to be about twice a hear it would do it, now it's about twice a week. I unlock it, get in, turn the key and nothing happens. The lights, stereo, dash lights, etc all come on but the engine doesn't turn over. I wait, play games with unlocking, locking, unlocking, moving gear shifter, locking, unlocking and all of a sudden it will turn over. This morning, it finally had enough. Now no matter how many things, or combination of what things it just won't turn over. Any ideas?