Why won't this GUI button work?

Expanding on my PM script, I made a button in a ScreenGUI that changes whether a person can received PMs or not. However, when the button is clicked, the value does not change and neither does the text. The output tells me nothing. Here is the script:

while true do
    if game.Players.LocalPlayer:FindFirstChild("PM") == nil then
        f = Instance.new("BoolValue")
        f.Name = "PM"
        f.Value = true      
        f.Parent = game.Players.LocalPlayer
    end
    wait(0.2)
end

function onClick()
    print ("hi")
    if script.Parent.on.Value == false then
        script.Parent.on.Value = true
        game.Players.LocalPlayer.PM.Value = true
        script.Parent.Text = "PMs Allowed"
    elseif script.Parent.on.Value == true then
        script.Parent.on.Value = false
        game.Players.LocalPlayer.PM.Value = false
        script.Parent.Text = "PMs Disallowed"
    end
end

script.Parent.MouseButton1Down:connect(onClick)

Can anyone help? The print doesn't show in the output either.