So this started around DP3... The dark "stitched" background of the login screen would show up but with nothing else (no username, wifi, shut down/restart buttons, etc.). I could login because you just type the password and hit enter, but you can't see it. Hulu wouldn't load, you couldn't use photoshop, youtube videos and other formats on the internet would appear see-thru (you would see the desktop wallpaper where the video would be in the browser), you had to use list view in finder (the icons wouldn't appear otherwise- you'd just get a white finder window. Also videos in OS wouldn't work (like how to scroll in lion video), and Safari tabs would just be white pages (I heard this happened alot)... Chrome works fine (although still not for videos). Still happened with GM, so tried re-installing. After reinstalling fresh copy of Lion (installed from USB drive onto newly erased HD) and getting user account back from Time Machine (I didn't transfer any old apps, settings, just the documents in case that was the issue), I restarted into Lion and it worked fine. The how to scroll video showed fine, all the above problems were fixed. Then I restarted Mac after installing some programs (perian, mojo, transmission, dropbox, air display, chrome- that's it), and it's happening again. I don't know what it could be. I mean Perian has graphical codecs but I don't see how that could cause all these problems. Anyone else have the same problem/ a solution? Thanks.