I fixed it, but it's not very clever on Operas part, but here's how I did it.
I downloaded a previous older version of Opera, version 40
I saved my bookmarks and completely uninstalled this ridiculous version 45, then used Crapcleaner to completely remove all traces of Opera. I went through my C drive manually too and took out everything.
Restarted my PC and installed version 40 and guess what? YouTube is playing fine now. I've disabled updates and won't be recommending Opera from now on until (or if) they fix these problems. It's ridiculous to go back to an old version to get an operational browser. Updates are supposed to be improvements.