You are referring to the green led light on the front of the machine that tells you the brush is rotating? this is operated by a small magnet on the brush roll, when rotating it generates a small current to bring the light on. Remove the brush roll and check for damage behind the green led inside the case, also check for the magnet on the brush roll, ensure it is not missing and the brush roll is in the correct way round, magnet needs to be at green led end (ie to the left)
Magnet is fitted flush within the brush roll close one end and is around 6mm 1/4" diameter.
Green light not working will not affect the machine in any way.