did u use google chrome to download the client ? if u did try with IE, this one have no problems.
do u get any error? if so, post an SS of it please.
even if ur antivirus expired its still running, just doesnt update. so try uninstalling the game, reinstall it BUT before you do any kind of updates create an exception on the antivirus for the whole folder u just created for the game.
make sure you have the last updates for graphics such as graphic card, directX, etc.
Let us know how it goes.