You either:
Returning LogOn.cshtm as partial from your action method (i.e., return Partial();)
or
Not specifying layout view for your LogOn.cshtm. If this is the case, specify a layout view in the _ViewStart.cshtml so that it applies to all pages by default OR specify it in the LogOn.cshtm itself using @ { Layout = "~/_Your-Layout-View.cshtml" } directive.