Brother 5240 laser printer changed toner still wont work.

When a brand new toner is inserted it has a switch that is activated when new cart is installed.

Machine has two toner light errors blinking is toner low, full on is toner out all stop,

 I guess yours has not reconised new cart, was it new out of a sealed box?

If so then it failed to reset upon install

You can pull apart reset lever on left front of cartridge and reset to original position if you want to get just a little tecnical

One sctew carefull gears fall off ,white lever needs to be fully to rear of slot to emulate new cart status..

If brand new cart return to supplier as faulty.

If you just refilled it, go buy a real one to prolong life of your product