Instructions
Put fresh batteries in the controller. If you're using rechargeable batteries, see if the controller works with standard disposable batteries. Ensure the light on the front of the controller isn't spinning (which indicates a weak battery) and that the signal is solid.
Move closer to the Xbox. If possible, position the Xbox so that the sensor is facing you with the disc tray in sight. Being more than 12 feet from the Xbox can cause interference. Also, disconnect any other 2.4 GHz wireless devices (such as phones and newer microwaves) from the area while using the controller.
Connect the controller to a different Xbox. If the controller has no issues on the alternate Xbox, the controller or the syncing mechanism on your Xbox may be malfunctioning.
Re-sync the controller to your Xbox. Press the "Sync" button on the front of the Xbox and press the "Sync" button on the top of the Xbox controller.