The change of value in the linked cell does not fire the Worksheet_Change event.
You could use the Worksheet_SelectionChange event but the 3 drop downs would not hide and unhide when the drop down 3 changes A11 until the cursor gets moved into another cell. This could leave things in the wrong state for considerable time.
I'd use the Worksheet_Calculate event. This requires making another cell somewhere on the sheet =A11 to make sure something gets calculated the instant the value in A11 changes. The Calculate event fires every time something, anything, on the sheet gets calculated so there is the potential that having this event do things could affect Excels performance in which case you could have the =A11 cell on a separate sheet with nothing else and move the code over to that sheet.

Right click on the sheet tab your drop downs are on, select view code then paste this into the sheet module that appears.