To confirm using the new remote model with fully charged batteries, when you press the power button you see the LCD display change, but the air con unit doesnt respond?
Assuming the above is correct, I would start by powering off the external heat pump and indoor air con unit for 5 minutes, then turn them back on and check if they are working.
With the unit on hold the power button on for 3 seconds and then see if the unit start working.
If this fails, it would suggest a remote sensor (IR) failure, and you will need to call out a engineer in order to check the resistance between the controller and IR LED, this is described on page 57 of the service manual here.
Please let me know how you get on