97 Nissan Pathy dies... HELP!

I have a 97 Nissan Pathfinder and have a problem with it dying after the engine warms up hot. When its cold i can start it right up and let it run for an hour or two but after it has warmed up for that long it shuts off. When i try to start it again it would just crank so i let it sit for about 10-20mins then it will start and run for another 5 minute and die. I had the car scanned and it showed up being a bad knock sensor.. so i replaced that and still doing the same thing. Now i went to scan it it shows: P0000 - systems checks Ok, 0 - Key cycles since failure. So now i ordered a crank sensor but i don't know that good that will do but does anyone have a clue what is wrong with my car? And what is: 0 - Key cycles since failure?