Mmm are u take any error in debug? if you did, show us to what is error. First, try to this:
 
	Change this your code in server-side:
 
function GUIness(player)
	local taccount = getPlayerAccount ( player )
	if isAdminAccount(taccount) then
		triggerClientEvent(player, "openGUI", player)
	end
end
addCommandHandler("balloon", GUIness)  --Command for opening GUI
	and change this in client-side, too:
 
function openGUI()
	if (cWindow ~= nil) then
		guiSetVisible(cWindow, true)
		showCursor(true)
	end
end
	 
 
	If it'll not work, send error to here.