Aircon doesn't respond to controller!

First, make sure that you've got new batteries replaced. It takes very little electricity to show the display on the remote
controller, doesn't mean the batteries are OK. The batteries may be too weak to send the signal across to the air

2nd :
The same brand of air conditioner usually have more than 2 different  types of remote controllers. If you got them mixed
up, they don't work.

Most air conditioners have a manual on/off button on the air conditioners. Most of them are inside the flap cover. Open
the flap first:

wall mounted aircon flap opened

Usually, the ON /OFF button is on the right side of the air conditioner:

aircon on off switch close up

Press the small little button, you may need to use a pen to press it. Does it work?

Either the remote controller is spoilt (test it on another air conditioner) or the infra-red signal receiver is faulty.
No : Either there's no power supply to the unit (check your circuit breaker) or there's a problem with your air
conditioner's electronics components or electrical cables. .