When you say it cranks, but does not turn over, does that mean that the starter does is not able to budge the engine, or are you saying that it is turning over but not firing. If it isn't turning over at all, I would think that it's either a dead spot on the starter motor. If it's turning over, but not firing, I would suspect something either fuel or electrical. When you first turn the key to on, you can have someone outside the vehicle listen for the fuel pump to kick on. If it does, then you are probably getting fuel. I would then begin looking at the ignition system.