Comment # 5 on bug 968889 from Wolfgang Bauer

(In reply to Radu M from comment #4)
> Got same issue. After clean installed on 2 PCs and applied updates got the
> same black screen after log in and KDE loading screen. I can see only the
> mouse cursor on a black screen.

This should be fixed already, just update your system again.

And rather see Bug#968877, this one has been marked as duplicate.