Instructions
Troubleshooting Wiimotes
Check the sensor bar's position and whether the wires are properly connected to the Wii console. The sensor bar should be sitting right atop your TV, and if it's off-center or not connected, it will not be able to sync with anything.
Center yourself exactly in front of the sensor bar on your television and hold the Wiimote out straight so that it's pointing directly at the television, then try to sync it again. It's possible the Wiimote was simply out of the sensor bar's range.
Remove any additional light sources from your playing area. Infrared light sources, meaning those that produce heat, can interfere with the Wiimote's sensing abilities. These include candles, stove tops and even very hot sunlight. Remove these sources, then re-sync the remote.
Turn all wireless devices off in the vicinity of the Wii. These include wireless laptops, cordless phones and cell phones, all of which can interfere with the Wii's frequency. Turning them off should clear the airwaves for the Wii. If this still does not work, then you might need to send your Wii into Nintendo for professional servicing unless the problem is unique among your Wiimotes, in which case the remote is probably faulty.
Troubleshooting Balance Boards
Check the back of the packaging for the game you are trying to use, and make sure it has the small Wii Balance Board icon on the back. If it does not, the game is not compatible with the balance board and will not sync up with it, as every game played must be individually synced to the board.
Insert the balance board-compatible game into the Wii's disc drive and point the cursor on the screen to the Wii's disc channel using a Wiimote, then press "Start" to begin. Press the "A" button on the Wiimote to bypass the redundant wrist strap warning screen.
Open the SD card slot cover on the front of the console, which should reveal the balance board's infrared sensor. If you could not sync the balance board before, it might have been because you had the sensor covered up.
Remove the battery cover on the bottom of the Wii balance board and press the small red "Sync" button beneath the case. A blue light on the board should begin blinking.
Press the red "Sync" button on the Wii console next to the SD card slot. If done at the same time the blue light on the Wii balance board is blinking, the board should sync to the console. If it does not after several attempts, then you will have to report the error to Nintendo and have the board or console professionally serviced.