I am posting this question in the MacBook Pro area but I have experienced this on an iMac as well. Also, this is not specific to a single Mac OS X version; on the MacBook Pro, I am on the latest version of Mavericks and on the iMac, I was on the latest version of Yosemite (the issue on the iMac was prior to El Capitan's release). It is hard to describe this error, so I will show it: Basically, any browser (this example is Chrome, which is worse, but it is similar in Safari) will redraw continually is basically unusable. In the video, I am not pressing any buttons, only moving the mouse around. The MacBook Pro had a boot hang on a grey screen for which I was able to remedy with the solution found here: http://apple.stackexchange.com/ques...-usb-drive-with-fresh-os-x-inst/144416#144416 While I don't want to jump the gun and send anyone who could help in the wrong direction, I believe that there is some issue with the graphics cards, specifically ATI cards. Both the iMac and MacBook Pro have those cards and it is basically the only similarity between the systems. I reiterate, it could be something else but this is all I suspect. Are there any solutions to this? Should I roll back the Mac OS X version so that older, better working drivers are used?