You have given us very little to work with, battery would be my first thought, check to see if 4.2 volts. Have you flown a heli before? Not meant to be offensive just not sure if you are doing it correctly. Did you do a preflight check to be sure servos are working and swash is level when powered up? Have you let the gyro stabalize before trying to fly?
What radio are you using? More info is needed to help steer you in the right direction...

Airshot