I get the impression the windows/widgets are there, it's just the screen that stays black.
Seen that behavior a lot ... especially after disconnecting the second screen i.e E27 should handle that 'on the fly' and move all the apps to the single leftover monitor.
It's definitely a bug but haven't yet found a sure-fire to make it come up, so that I can report it to the enlightenment devs. 
It has been reported none the less.
E27 has other tricks than most, in the way that a restart can be done by Ctrl, Alt + End combo ... which by the way will be only effective if it has crashed or frozen over. The same goes for hitting Ctrl, Alt + F1 for a tty. On a normal running E27, that's impossible, it works only if E27 is having issues. 
Tip:
If you can log into a TTY then the command: enlightenment_remote -restartwill also restart E on where you left it, usually TTY8 .
In addition I just discovered that if I stop/start or simply start an app (I've got 'guake' under F12), it shows the desktop too.
Anyway, the way to go for E27 bugs: