How to make screengui enable through this short script?

while true do
for i,plr in ipairs(game.Players:GetChildren()) do
        local char=plr.Character
        print("works")
        if char~=nil then
            local t=char:FindFirstChild("Torso")
            local h=char:FindFirstChild("Humanoid")
            if t~=nil and h~=nil then
                if h.Health>0 then
                    pos1=t.Position*Vector3.new(1,0,1)
                    pos2=script.Parent.Base.Position*Vector3.new(1,0,1)
                    if (pos1-pos2).magnitude<10 then
                        print((pos1-pos2).magnitude)
                        print("I'm close enough")
                        game.StarterGui.ScreenGui.Enabled=true
                        print("Screengui should be enabled")
                    else
                        print("I'm not close enough")
                        game.StarterGui.ScreenGui.Enabled=false
                        end
                    end
                end
            end
    end
wait(1)
end

What this script does is checks your distance every second, if the distance is less than 10, a screen gui should enable, but it doesen't - any idea why?