Here is the synopsis of the problem….
You have a cell setup as a pull down cell (Data Validation in Excel terms) but you do not see a pull down arrow.
And you cannot manually change the cell value as it has Data Validation enabled on that cell.
How do you enable the Data Validation (drop-down menu) arrow button
1) Click the Office Button, then click Excel Options.
2) Click the Advanced Category
3) Scroll down to the ‘Display Options for This Workbook’ section and under ‘For Objects, Show’, select All, then click OK.
Here is a vlog of how you can enable the Data Validation (drop-down menu) arrow button