I know this is an old post.. but for future reference...
If one or more of the motors or ESC is shorting out. Open her up and see if there are cables that have melted together and causing the short.
And if it isn't... try method of elimination -
Take photos before attempting so you can reverse what you have done.
Try removing the M1-M4 4 pin connector on the NAZA and then try to power up the P2. If this powers up the P2 then plug it back it in and make sure its in the correct way as this will cause the P2 to flip if the cable is installed upside down.
Then try removing the molex connectors on each of the ESCs. It should just unclip and they are labelled M1. This will then tell you which motor is failing. You can look closely at the mosfet chips on the ESC and see if any are burnt out.
If this all fails - look for the most damaged motor or esc board and cut the wire (I find it easier to solder cut wires) and try powering it up. Repeat until you can find the faulty motor.
