Verify the power cord is not damaged and is plugged in. Also check the fuses on your pcm as one of them may be blown. Refer to the service manual. (MAN112 for A-L models and 147605 for M and newer)
It may be that the gas cylinder is worn out and needs to be replaced. Refer to service manual 144386.
It may be that your Trendelenburg gas springs are worn out and need to be replaced. Refer to service manual MAN272.
The control box or the actuator may be faulty. You can swap the foot and head connections on the control box to indicate which part needs to be replaced. Refer to service manual 151184.
All Hillrom® products come with a Service/User Manual at time of purchase. New Service/User Manuals can be ordered by contacting Tech Support at (800) 445-3720.