DIAGNOSIS
The infrared pairing link between the remote and the machine has been lost. This can happen after a battery change or power surge.
FIX
1. Remove the remote's battery for 30 seconds.
2. Point the remote directly at the infrared sensor on the machine's base (next to the power cable port).
3. Press and hold the 'Temperature Up' (+) and 'Oscillation' buttons on the remote simultaneously for 5 seconds.
4. You should see a red light flash on the remote and the machine will chime, confirming re-pairing.
IF THAT DIDN'T WORK
The issue may be with the machine's IR receiver. Test the remote on another Dyson device if possible. If the remote is functional, the HP07's receiver board may need service.
HEADS UP
The remote uses a clear line-of-sight infrared signal. It will not work if the sensor on the base is obstructed or if you are pointing it at the wrong part of the machine.