Some more information would be appreciated. Do you mean that the cursor still flashes but none of the buttons work? You may want to try replacing the batteries including the backup battery with fresh ones.
If you get a constant, solid black screen when you turn it back on, press [2nd] then release it, then hold the down arrow key until the contrast is where you want it.
Have any of the [[Topic:Texas Instruments TI-83 Plus|guides for your calculator]] helped?