Why doesn't my TI-84 calculator turn on

Perhaps the batteries died or corroded? You should open up the battery compartment to check if there are any corroded batteries. If there are, carefully remove them, clean up the connections in the battery compartment, and add fresh batteries. If it still doesn’t work, there may be damage to the motherboard from the corroded battery. You can try this guide to replace the motherboard.

If the batteries are completely fine, then you may want to refer to this amazing wiki. If it doesn’t help, you can see if your calculator still has life in it by pressing the [on] button (with batteries) and connecting it to a computer using a mini USB to USB cable. If your computer recognizes that something was plugged in, then it’s most likely the screen that has failed, the guide I linked above will help with replacing the screen. If your computer doesn’t recognize that something was plugged in, then I’m sorry, but your calculator is toast. You’ll have to contact Texas Instruments support and see if you can receive a working calculator.