Private Sub Worksheet_Change(ByVal Target As Range)
Application.EnableEvents = False
If Target.Address = "$A$1" Then
Select Case Target.Value
Case 1234
MsgBox "Welcome John Doe"
ActiveSheet.Unprotect password:=""
Case 5678
MsgBox "Welcome Jane Smith"
ActiveSheet.Unprotect password:=""
Case Else
MsgBox "Invalid employee number, please try again"
End Select
End If
Application.EnableEvents = True
End Sub