How do I create a Yes/No Drop down list

To create a drop down list do the following:
Crate a list of entries you want to appear in your list (In your case Yes / No) either in the same worksheet or an additional worksheet.

Click in the cell where you want the drop down list to appear.

On the toolbar Go to Data > Validation
In the allow box choose List then select the cells that have your values (Yes/No) from the source window
If you require any other validation information select it from the other tabs else click ok
Click in the cell and you will see the two selected values

Don't know if it will sort all your problems but it works.