checkbox uncheck for windows 8.1 phone app

I have a control checkbox that allows the app to play sounds (SoundEnableBox) when it is checked. If they uncheck it I want it to stay unchecked (So I need to programmadigally uncheck the box when the page is reloaded. The default is set to checked. Every time the page is reloaded it gets checked again.

I tried the following code but it is not working. Do I need to bind the property? to keep it unchecked?

if (GlobalVariables.SoundsEnabled.GlobalBool == false) {

            SoundsEnabledBox.Unchecked = true;
        }

I know this should be simple but not with windows phone for some reason.