Vba to protect the cell

The default for cells is locked, so first unlock all the cells.

Click the empty grey box between the colmn & row headers to select all cells -> Format -> Protection -> uncheck Locked. Then use this code

Option Explicit

Sub Button1_Click()
    Const PW   As String = "secret"
    Dim rNonBlanks As Range
    On Error Resume Next
    Set rNonBlanks = ActiveSheet.UsedRange.SpecialCells(xlCellTypeConstants)
    On Error GoTo 0
    rNonBlanks.Locked = True
    ActiveSheet.Protect PW
End Sub