It won't fire or it won't crank at all?
If it won't crank, take your multimeter and trace the wires to figure out what's not getting power. Don't trust fuses that look good, test them. Make sure you have 12V at the battery. Make sure you have 12V at each fuse with the key turned on.
If it won't fire, check the four basic components: spark, fuel, air, and compression. If you have those four, you'll have a running engine.