Arduino mega + shield controler motior: reset automatic

Hello,
It's my first post un this forum ! I havé à probleme with my Arduino mega + shield 2cc motor and a keypad.
Everything is ok when i use the USB of my computer. When i put the right password on my keypad, the shield start my motor 5 secondes.
But if i put my arduino with, only, a battery of 9V.. when I pur the right password, my Arduino reset automatically..
Sorry for my bad English

A PP3 battery? If so my guess is that the motor is drawing more current than the battery can supply.

Either get a bigger battery (6 x AA) or a power supply.