Launched seven years ago in March 2007, justin.tv has been shut down, handing over the reins to the Twitch service and brand, which became "the focus of the company's resources" in February 2014 on the replaced official page of justin.tv.
If you have an account on justin.tv, it's been closed and you unfortunately don't have access to it nor are they available for download. You can complete this form to have your account transferred to Twitch for the full site, so long as it's filled out by September 5.
If you're a Pro Account User, you should have already received an email about getting refunded. They certainly wish for you to use Twitch.tv, but they also recommend Ustream, Livestream, and YouTube, whose parent company Google purchased Twitch for $1B in late July.