private void YourEventHandler(object sender, KeyEventArgs e)
{
if (System.Windows.Input.Keyboard.IsKeyDown(System.Windows.Input.Key.S) &&
System.Windows.Input.Keyboard.IsKeyDown(System.Windows.Input.Key.LeftCtrl) &&
System.Windows.Input.Keyboard.IsKeyDown(System.Windows.Input.Key.LeftAlt))
{
}
}