You have to turn on your transmitter first with the gyro switch in heading hold. Next turn on the heli, and don't move the heli until the red light on the gyro stops blinking. At this stage the red light will be on constantly, next you turn the gyro switch to normal mode, hover the heli and trim the tail rotor. When you are happy with the trim land the heli and flick the gyro switch between normal and head hold three times quickly, stopping in the hh position. At this stage the red light on the gyro should be a constant red light again. Now hover the heli again in hh mode and the trim will be set.

You have to always turn the heli on in the hh mode and don't move the heli until the red light becomes constantly on. If it doesn't stay on constantly you have to turn it off and start over again.
I have 2 gy401 gyros and haven't had any problems.

Sparkhead