On Xubuntu 14.04.3 LTS I got a black screen after wakeup the machine from suspend mode. This didn’t happen all the time. It was more of a sporadic phenomenon happening after entering the credentials to unlock the machine. Under these circumstances the screen got black and the machine didn’t react on any actions any more. I could got to the shell with CTRL+ALT+F1 and back but I didn’t get to the desktop anymore.
After searching around the internet I found a official solution tutorial on xubuntu.org. But otherwise than as described the problem wasn’t fixed on my machine although the Xubuntu version is higher than 14.04.1 where it should have been solved.
That’s why I had to fix it as described for older versions: