ARDUINO motor shield not working

Hi

Iam using Arduino mega2560 and official arduino motorshield to control the speed and direction of two dc motors. The motors are running if power supply is given directly. The motors are rated for 7.2v. When the motors are supplied through the motor shield they are not running. Moreover i can hear a humming noise when connected through Motorshield. i am providing power supply from a 11.1v Li-po battery to the motorshiled. The PWM value i am giving is 150. Both the shield and the arduino mega2560 are getting powered up but the motors aren't running. The indicator leds on the shield are also not glowing.

I have cross checked the code several times to make sure all the pin assignments are correct. All those seems correct. But still motors are not running and making a humming sound.

Someone please help me...

What's the current rating for those motors ?

Loads like these need a much higher current to start than what they need to keep running. But you need to make sure the shield can handle the needs of those motors. Current is much more important than voltage (within limits of course).

Don't expect the official motor shield to drive high current motors, it won't.