Things to check if you are unable to connect to the RCE:
Is there an active outage? All outages are posted to the outage notifier (the widget in the top right of your RCE session), the RCE calendar, and to our outages mailing list in advance of planned maintenance windows. You can also check the HMDC status page. For more information, visit our RCE outages page.
Are you over quota? If your home directory goes over 2GB, you won't be able to log in to a RCE desktop. Log in via SSH to clean up your home directory. See, How Do I Check My Quota? for more information.