local gui1 = game.StarterGui.TeamChange.Frame.TextButton
gui1.MouseButton1Click:Connect(function() game.Players.LocalPlayer.PlayerGui.TeamSelector.Frame.Visible = true end)
"TeamChange" Is a ScreenGui
The "TeamSelector" is a ScreenGui The Frame in "TeamSelector contains multiple TextButtons

3 comments
Are you using a local script or no?
http://wiki.roblox.com/index.php?title=Player_vs._Starter_GUIs
http://wiki.roblox.com/index.php?title=API:Class/PlayerGui