How do i make a GUI only visible to People With a certain Rank?

Your method of disabling the GUI is not at all adequate as the client could easily enable the GUI or avoid touching the brick. You also gave multiple errors in your code such as flipping your sign and not spacing properly.

Instead of doing what you did, I will create a table for all the ranks that are allowed to get the GUI, and only insert the GUI into those who are the proper rank.

In order for this to work you must NOT place the Gui in StarterGui, you must place it inside of this script. This script should be placed inside of ServerScriptService.

Ranks = {16,17,252,253,255} -- Allowed ranks
GroupID = 4126160

GUI = script:FindFirstChildOfClass("ScreenGui")

Players = game:GetService("Players")

Players.PlayerAdded:connect(function(Player)
    if Player:IsInGroup(GroupID) then
        local Allowed = false
        for _,Rank in pairs(Ranks) do
            if Player:GetRankInGroup(GroupID) == Rank then
                Allowed = true
                break -- Stop searching
            end
        end
        if Allowed then -- If  allowed to see the gui
            local NewGui = GUI:Clone() -- copy of the GUI
            NewGui.Parent = Player.PlayerGui
        end
    end
end

I hope I helped! Let me know if you have any questions.