Hi, This just happened today. I closed AD, restarted, didn't happen in the beginning. Afterwards it did again for a while. Now it's over again. I remember a month ago,I had some issues to. There were stripes and glitches across the screen really badly for like 10 secs. It's a brand new Imac, 21,5/3,3ghz/16gb ram and a fusion drive. Has something to do with affinity? I was using a wacom tablet that was charging at the keyboard and I have a harddrive for backups attached. No other programs except email was open. I'm new to Imac. So not sure if this happens sometimes or if it's really bad.