1) Take it apart and attempt to diagnose and repair it
2) Have someone else diagnose and repair it
3) Buy new mixer
4) Make do without.
Depending on the nature of the fall the damage may be minor (broken conductor in power cord) or major (motor or gearbox cracked in some way)
Only by looking into it can you determine which it is.
Good luck...
Peccavi
February 2013