Maintenance for the week of January 19:
• PC/Mac: No maintenance – January 19
• NA megaservers for patch maintenance – January 21, 4:00AM EST (9:00 UTC) - 10:00AM EST (15:00 UTC)
• EU megaservers for patch maintenance – January 21, 9:00 UTC (4:00AM EST) - 15:00 UTC (10:00AM EST)
I got that trying to queue from Cyrodiil to Imperial City. After waiting a bit, I decided to end the rask, but just as I was about to end the task I got a loading screen, then after a short pause I arrived in Imperial City.
I just went to queue from Imperial City to Cyrodiil and saw that it shows me as being already queued for-- or possibly in the process of entering-- my home campaign, as though that message had never gone away from the last time I had queued for Cyrodiil. I tried to leave the queue but couldn't, so I queued for a different campaign. Then I got the black screen again, but I decided to just wait it out, and eventually I got a loading screen and arrived in Cyrodiil.
So my advice would be to wait it out rather than force-quitting.