Why it doens't make the gui visible? No errors?

So i want if it's a player you get the gui else not? I did this but it isn't working?

local player = game.Players.LocalPlayer
local mouse = player:GetMouse()
local target = mouse.Target
local open = false

mouse.Button1Down:Connect(function()
    if target and game.Players:FindFirstChild(target.Parent.Name) then
        if open == false then
            script.Parent.Main.Visible = true
            script.Parent.FillTarget:FireServer(target)
    elseif open == true and not target then
            script.Parent.Main.Visible = false
            open = false
        elseif target and open == true then
            script.Parent.FillTarget:FireServer(target)
        end
    end
end)