I already answered this on the TI 84 Plus forum, but I’ll copy and paste it here.
This isn’t suppose to happen, you may have changed a setting that affects this and you can fix it by reverting all the settings back to their default by:
* Press [2nd]
* Press [+]
* Press [7]
* Press [2]
* Press [2]
Your settings should now be back to their defaults.
If that doesn’t work, perform a RAM reset by removing the batteries (including the backup battery) then reinserting them.
If ''that'' doesn’t help, try to reinstall the OS. This is more complicated so I’ll refer you to a video tutorial [https://youtu.be/8HlPgS0elRM?t=10m22s|here].
In the extremely unlikely event that nothing worked, [https://education.ti.com/contact-us|contact TI].