Out of toner, when it isnt!

Depending on the kind of copier, all copiers have toner sensor. The sensor flip or botton is out of position. When a toner is inserted in a copier, it is either displacing a flip which open light to a sensor or pressing a sensor botton. In either case a signal in sent to the processor that there is toner or not. Check in the toner chamber, you will it either blocked with dirt. First try power cleaning "Use air preasure".