Upgrade from 14.04.5 to 16.04.1 failed

Through the installation it notified me that the upgrade failed due to too many errors and it aborted. I powered off the machine and now I can't boot into my system.

When I try to boot I see a black grub screen. Then Plymouth shows the ubuntu studio boot screen. Then that Nvidia logo flickers a bit, then a black screen and nothing happens.

Long ago I've followed some guide to get the ubuntu studio applications into my normal ubuntu.

Luckily I've made a clone of 14.04 but for some reason I can't boot into it either. This makes me assume that my main problem is related to grub hopefully.

I don't know what kind of information do I need to provide. I have a 16.04 live usb ready. What files do I need to provide?

Edit: here's the paste created by bootrepair http://paste2.org/h4ULxpeM

Update: Command used to get ubuntu studio applications:
sudo apt-get install ubuntustudio-desktop

Now the backup-ubuntu boots fine. I think I was booting grub in legacy mode the whole time & when I tried uefi mode it worked. But still the half-upgraded ubuntu is not booting. Same symptoms.