I've just installed Ubuntu 16.04 LTS on my iMac 21.5 mid 2010.
I've followed this guide:
http://www.macworld.co.uk/how-to/mac/how-install-linux-on-mac-3637265/
The installation went perfectly, but when I rebooted it gave me the "Remove installation problem" error . So I manually rebooted my machine. I then received a purple screen and then a totally black screen appears. After a few seconds I heard the sound of ubuntu (the drums thing) but nothing appears on screen.
Does anyone know what the problem is and how can I fix it? It's my first installation of Ubuntu and I don't know what to do...