Files are pixilated on the new Illustrator

I have recently downloaded the the new version of Illustrator onto my new Mac and I have opened files from my hard rive (which have also been created in the new version of illustrator) and the lines and fills are all pixilated and keep moving as i move the mouse - its like the program is struggling to keep up? I'm not too sure why this is happening when they are from the newest version?

I have attached a picture below of what keeps happening....

please help!