I have protected the sheet. Now I want users to be able to insert from the
drop down list. But once inserted, they should not be able to delete it.

Eg - my drop down list has the option only to select "YES".
Once the user selects YES and saves the file, nobody should be able to
delete it.

It is a shared workbook and 5 users would be using it at the same
time...which is why, I do not want any tampering with this data.

Senario - When clients walk in, if their names exists in the data base, the
user will select "yes" and move onto the next customer.