The TI 84 has battery-backed storage. If you replaced the backup battery, or it has died, you may not have any data to recover. You can’t chip-swap it, since that would also lose the battery power. It seems that, to get inside the device, you’d end up disconnecting all batteries.
Here is a video that may help revive it, but would still lose any data on it.
https://www.youtube.com/watch?v=jxHstNp939A&ab_channel=BarTechTV