Hello. I'm having a very strange problem with my Mac lately. When I'm working in an app and a new window pane or sheet is displayed, sometimes it comes up completely white. Once an app is having these problems, it will continue to bring up a blank screen for that particular window (although other windows work fine). After the app is relaunched, the window is fine again. What I'm noticing that's very strange is that although the interface turns completely white, the functions of the interface are still available. So I have to "navigate blindly" around the interface, until I can relaunch. This occurs throughout the operating system. Screenshots: This is what happened when I tried opening the File menu in Lightroom app. What happened to me on Lynda.com (in Firefox) after selecting the "Software..." dropdown. (All other dropdowns were fine. Reloading the page fixed it.) When I was decompressing a file, The Unarchiver launched and opened this white window. It still decompressed the file. This is what happened one time when I opened Finder (with TotalFinder) to my Downloads folder. This is something I've never seen before. This just started happening lately. What could be the problem? Thanks for your help. NOTE: since new users are not allowed to post images, just image blank white interface elements. And since new users also aren't allowed to post more than one link, here's the first screenshot: