Data validation dropdown list isn't working

srugh I can't say that I have. One possible cause is that objects have been hidden for the entire workbook. Go to File > Options > Advanced, then scroll down to "Display options for this workbook:" and make sure "All" is selected under "For objects, show:".

Advanced Options

It's also a good idea to double-check the data validation rules to make sure "List" has been selected and the "In-cell dropdown" checkbox has been checked.

Data Validation List

If indeed the settings are correct, try clearing the data validation rules and recreating them from scratch.

Lastly, if Freeze Panes has been applied to the neighboring column (on the right) and the horizontal scroll position is too far to the right, the drop-down arrow may appear to be missing when all you need to do is scroll back over to the left.

Freeze Panes: Column D hidden by horizontal scroll position

If none of these suggestions apply to your situation, it's possible the workbook has become corrupted. You could try restoring the file from a backup (if available) to see if the problem exists in a prior version of the file; or, try recreating the data validation rules in a new worksheet to see if the problem persists.

Kind regards.