Please be aware that it may take long to load the game for the first time. So if it seems to you, that the progress bar stays put, try to be patient and wait for a while. The loading time may also increase after the maintenance.
If you're absolutely sure, that the game has stopped loading, try clearing Unity Player's cache (here's the link) as well as the cache of your browser. You can also try to reinstall your browser and Unity Player.
If this recommendations won't help, please submit a ticket to our Support Service.