Batteries Dead
The batteries in the Wii remote may be dead. One of the blue buttons along the bottom of the Wii remote will blink if you attempt to turn on a remote control with dead batteries. Make sure the batteries are either new or charged to ensure you get the longest life from the batteries.
Sensor Bar Not Set Up Correctly
Disconnect the Wii sensor from the back of the Nintendo Wii, wait for a minute and then push the connector back into the Wii firmly to ensure it is connected. Position the Wii sensor bar either directly above or below the TV in such a place that your Wii remote has a clear path to it so it can pick up a strong connection.
Re-Sync Remote with Wii
Take the batteries out of your Wii remote and then wait for at least one minute if you feel like the batteries still have some life in them. Put the batteries back in the Wii remote and then wait another minute. Press the "Power" button on the Wii remote to turn it back on. Press the red button that says "Sync" directly beneath it beneath the batteries. Open the small cover to the left of the middle of the optical drive on your Wii console and press the red "Sync" button. The remote and your Wii are now re-synced.
Clear Wii Synchronization Memory and Re-Sync
Shut down the Wii and disconnect the power cable from the Wii. Wait for 30 seconds and then reconnect the power cable to the Wii. Press the "Power" button to turn on the Wii. Open the small cover to the left of the middle of the optical drive on your Wii console and press the red "Sync" button and hold it down for at least 15 seconds to clear all synchronization information associated with your console. Press the red "Sync" button on the front of the Wii console again. Remove the battery cover from the back of your Wii remote and then press the red "Sync" button beneath the battery bay to sync your Wii remote with your Wii.