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.