Question: I had a windows 7 and Ubuntu 14.10 then i upgraded windows 7 to 8.1 now I cant get Ubuntu to boot

I now have grub but grub will not find Ubuntu

<http://paste.ubuntu.com/11019932>

Answer: 
I think the problem is with the NVidia driver and the use of OpenGL.
When you experience the black screen login on to an other tty and try the following:
- sudo vi ~/.config/kwinrc
- Change Backend=OpenGL to Backend=XRender
- then restart with kill -9 -1

You should now be able to login using Plasma.
It is however very slow but you can sometimes switch back to OpenGL. If you can switch you'll have the performace you expect from Kubuntu.

Before shutting down don't forget to switch back to XRender or you will have to repeat the same steps.
The nvidia-304 drivers will work with Kubuntu 15.04 if you disable the Compositor in System Settings->Display and Monitor