It sounds like the "Enable fill handle and cell drag-and-drop" option may have been turned off in Excel. Here's how to turn it back on:

1. Click on the Office button (the round button in the top left corner of the Excel window).
2. Click on the Excel Options button at the bottom of the menu.
3. In the Excel Options window, click on the Advanced tab.
4. Scroll down to the "Editing options" section.
5. Make sure the "Enable fill handle and cell drag-and-drop" option is checked.
6. Click OK to save the changes.

If this option was already checked, it's possible that there is a problem with your Excel installation. You may want to try repairing or reinstalling Excel to see if that fixes the issue.