I am working with a workbook that has one worksheet only. I want all rows
visible when the user opens the file. However, In cell B10, I have a
drop-down list I'm generating with data validation. The only values are YES
or NO, and YES is initially selected. If the user selects YES, then I want
the entire worksheet to remain visible. If the user selects NO, then I want
to hide rows 11 through 50, and display an error message entered in row 51.

Using previous posts, I've begun the code, but I know it's missing some
things.

Private Sub Worksheet_Change(ByVal Target As Range)
If Target.Address = "$B$10" And Target.Value = "YES" Then
Range("B11").Select
ElseIf Target.Address = "$B$10" And Target.Value = "NO" Then
Rows("11:50").Select
Selection.EntireRow.Hidden = True
Range("A51").Select
End If
End Sub

Any help you can give me would be greatly appreciated.