Read this: http://members.xoom.com/tifaq/#8. >I have a classroom set of 30 TI-83 calculators. In the last three weeks I have >had 2 of them become unusable because when I put in the batteries, and turn >them on the screen comes on totally black and I can't turn them aff or adjust >the darkness. Is there something I can do to fix this problem? I really need >to have all of them working when everyone is there.