we are currently making the quadcopter using pixhawk flight controller. for fly drone we follow all the necessary step starting from  as below,
accel calibration,compass calibration,esc calibration,radio calibration. we are using the mission planner for auto mode also for that we have implement telmetry and gps as well.
after doing all the thing we finally achived the proper flight and accidently we crashed our quad.no parts broken but when we next time tries to fly quad one of the motor isn't able to lift the quad while other three working well. so after that we replace the motor with new one so problems seemed to be solved. but once again we crashed the quad and this time two motors isn't able generate the required thrust. so what is the resason behind this? why motor isn't generating proper thrust after crash?
we have used a2212/13t 1000 kv motor
battery is 2200 mah/25 c
esc is 30 amp

How do you crash ?

Post crash video for analysis.

Motor or ESC could have probably damaged.
Did you try to run the motors separately i.e directly hooked to receiver through ESC? How do they perform compared to other motors?

Can you post pictures of motor and ESC. Let us know which brand components you are using.
Not all brands made equal and some ESC tend to damage during shocks/crashes

OR post a log (.log or .bin) file of the 'crash flight' and the 'last flight' from the FC.