Manuel,
First we need to make a distinction between "Crank" and "Start". Do you mean the engine does not rotate when you engage the starter via the ignition switch, or that it won't start and run?
If it's doing nothing when you turn the key, check for loose connections at the battery and starter. Also check your fuses in the car and under the hood for any that may be blown.
If the engine is turning, then you need to check to see if you're getting spark and fuel. Without these two thing the engine will not start.