Hi everyone Yosemite beta has been pretty bad for me :-( I installed the public beta 4 days ago. I had the same problem a lot of people are having - it took 3-4 hours to install on my early 2011 MacBook Pro (with 80gb free space), with no indication of what was happening. Once it installed, it went badly wrong. I cannot log in. The login screen flashes every 2 seconds, as if it's a TV being tuned in. Then it goes back to the login screen. There's a permanent spinning ball. I can type my password (although it takes minutes for the letters to appear in the password box) but nothing happens after I press enter. I've waited for a few hours. I can log in with Safe Mode - although when I log in, I get the 'processing' icon (the one with thin lines in a circle like a clock), often for 3-5 minutes. But once it logs in it's a disaster area. Most programs are unstable - I don't know whether that's cos of the restrictions of Safe Mode or whether it's part of the same problem: Browsers can only use basic fonts, I can't watch any video, iMessages is taking 48 hours to display messages, Safari won't load, pages won't load in Chrome; spotlight won't display any apps. Finder crashes all the time - in fact if I load up Activity Monitor, there's always at least 4 apps 'not responding' - SystemUIServer, iCloud Photos, loads of things. The system is unstable - sometimes it simply stops working. Can anyone give me any advice please? I believe I've reset PRAM and NVRAM. I've been hunting for people who have had the same problem, but haven't had any luck. Here is the video (just a shot of the screen): http://youtu.be/tx5PYswzLAc I've got a full backup, I'm not worried about that. The downside is, I had to leave my house to look after a sick relative, so I've got to live with this install for a week. Has anyone experienced the same problems? Is there anything I can do with this installation, or am I screwed and need to reinstall Mavericks from scratch? If that's the case, I'd really appreciate it if people could point me to an easy-to-follow guide showing how to revert back to Mavericks - I just want to make sure I don't mess up the reinstall. Thanks for your advice everyone. I've never had this kind of problem from an Apple beta before. I'm not criticising Apple for this - I knew what I was getting into and I'm secure with everything backed up. It's just a pain that I've got to wait a week before I'm able to reinstall. So, any advice on how to fix the bad install would be really appreciated.