Put this code in the Thisworkbook Code Module and delete all the Worksheet_Change in all the worksheets
Option Explicit
'Insert a sheet named "MacroWarning", with a note to allow Macros on it.
Private Sub Workbook_BeforeClose(Cancel As Boolean)
Sheets.Visible = False
Sheets("MacroWarning").Visible = True
End Sub
'This sub only runs if Macros are enabled
Private Sub Workbook_Open()
Sheets.Visible = True
Sheets("MacroWarning").Visible = False
End Sub
Private Sub Workbook_SheetChange(ByVal Sh As Object, ByVal Target As Range)
Dim cl As Range
Dim Check As VbMsgBoxResult
Sh.Unprotect
For Each cl In Target
If cl.Value <> "" Then
Check = MsgBox("is this entry correct? This cell cannot be entered after entering a value.", vbYesNo, "Cell Lock Notification")
If Check = vbYes Then
cl.Locked = True
Else
cl.Value = ""
End If
End If
Next cl
Sh.Protect
End Sub