try it with it on the bottom or the top, whichever one you dont have. but make sure you change the settings in the Wii's configuration.
then you have to adjust the distance from it. note, the sensor bar only detects where you point the wiimote, not the actual motion sensing. if all else fails, i heard you can use two candles as a sensor bar, seeing as the sensor bar is only 2 LED lights for the wiimote to detect.