Helicopter NR and N2 - Low. PLease help

Hey guys,
Am normally a fixed wing jock on the sim but have been messing with helo's recently but I have a problem that when I do a cold start and sometimes when swapping between helo's (and fixed wing) that most of my choppers have very low NR's and N2 which means I generally cannot get lift. Ok I have tried shutting down and restarting but to no avail and I have the turning knob that would be asociated with prop pitch (on fixed wing) etc set at the correct setting... someone please tell me what I am doing wrong.
Am normally a fixed wing jock on the sim but have been messing with helo's recently but I have a problem that when I do a cold start and sometimes when swapping between helo's (and fixed wing) that most of my choppers have very low NR's and N2 which means I generally cannot get lift. Ok I have tried shutting down and restarting but to no avail and I have the turning knob that would be asociated with prop pitch (on fixed wing) etc set at the correct setting... someone please tell me what I am doing wrong.