It is very easy to accidentally delete your L1, L2, etc from the TI 83 or 84. But, it is also very easy to get it back! Anytime your L1 “disappears”, simply press the [STAT] button, select “5: Set up editor” and press enter. The screens should look like this.
How to Prevent This From Happening Again
Anytime you need to get rid of data in your calculator, highlight L1 or the list name, and press [CLEAR]. It’s pressing delete that will remove the list from your editor.