Welcome to IRO! I just double checked and noted the client for the discontinued Transcendence server is still linked on the website. So please make sure you were looking in the right spot, since you'd want to use the client which is downloaded from this page.
So if you had mistakenly downloaded the client for the Transcendence version of the game, which has now been discontinued, then you'll want to try again with the downloader fro the link above. Once you have it installed and it finishes patching it should have a Play button in the patcher and then you can login at that point. When making your characters I would recommend the Chaos server as it does have a more active player population but Thor also can be a great option too, especially if you already have friends to play with.
Hope this helps and see you in game!