Lists are Missing in the Data Entry Screen
Sometimes a list, like L1 or L2, may disappear from the data entry screen. In this case, press STAT and use the down arrow to move the cursor to SetUpEditor. Then press ENTER twice. If you press STAT and ENTER, the missing lists should be back in the data entry screen with whatever data was in them when they disappeared.
Error: Dim Mismatch
If you are working with two lists, make sure each list has the same number of items. If you are trying to plot, make sure you the plot you want is set to On. Sometimes when lists disappear, a person will try to rename the remaining lists so the remaining lists are L1, L2, L3, etc. The result looks good, but the calculator uses the original list identities even if you cannot see them. So if the number of items in each of the original lists do not match, you will see the Dim Mismatch error. To see if there are missing lists, use the method described in the paragraph above.
Nothing Seems to be Work
If your calculator is stuck at some point, and nothing you do seems to improve the situation, try pressing 2ND and MEM. Then use the down arrow to move to the Reset… option and press ENTER. Choose Defaults and press Enter, then choose Reset and press Enter again.
If this does not work, you might try choosing ALL RAM instead of Defaults in the above sequence.
If this also does not work, you might try to find someone more technically competent than me or try the Texas Instruments customer support website,