Try Another Remote
The first thing you should check is that the remote is malfunctioning and not some other part of the system. In order to do this, attempt to connect another remote to the Wii. If another remote can connect to the Wii, then there is a problem with the remote, not the Wii.
Replace the Batteries
Since the Wii remotes require batteries to operate, try replacing the batteries. The battery pack is on the back of the remote. The Wii requires two AA batteries.
Retry the Bluetooth Connection
With fresh batteries, the only other option is that the Wii remote is not properly synced to the Wii. Try to resync the Wii to the remote. You need to press the sync button on the Wii (which is near the SD card slot) and then press the sync button on the Wii remote (which is near the batteries).