Lock all the cells of a worksheet when specified text entered

Question

I have an Excel sheet which has fields to enter data.

Let's say the total fields is 20. Ten of them are locked by default whenever the user opens the workbook. Now, one of the fields is asking the user to enter a password. If the password was "AAA", then five fields (of the ten locked ones) will be unlocked . If the user inputs a password as "BBB", then all the cells of the worksheet will be read-only and locked.

I am focusing on the case when the user inputs "BBB". I tried this code:

if Range("Password").value="BBB" then
 cells.select
 selection.locked=true
end if

It gives me an error as " Overflow".

Answer 1

If Range("Password").Value = "BBB" Then
   ActiveSheet.UsedRange.Locked = True
End If

Answer 2

It gives me an error as " Overflow".

I doubt you should get an overflow error with this code. An overflow may occur if you use something like Cells.Count in Excel 2007 onwards. CountLarge was introduced just because Cells.Count returns an Integer value which errors out in Excel 2007 because of increased rows/columns. Cells.CountLarge returns a Long value.

Now back to your query.

You do not need to SELECT all cells. In fact you should avoid the use of Select. You may want to see How to avoid using Select in Excel VBA

Also locking all the cells of the worksheet will be ineffective if you do not protect your worksheet. You can change your code to

If Range("Password").Value = "BBB" Then
    With ActiveSheet
        .Cells.Locked = True
        .Protect "Password"
    End With
End If

And if you do not want to use Activesheet then use something like this

Option Explicit

Sub Sample()
    Dim ws As Worksheet

    '~~> Change this to the relevant sheet
    Set ws = Sheet1

    With ws
        If .Range("Password").Value = "BBB" Then
            .Cells.Locked = True
            .Protect "Password"
            '~~> To unprotect, uncomment the below
            '.UnProtect "Password"
        End If
    End With
End Sub