First things first, let's get it out of the way: I'm an idiot. I installed the Yosemite beta on my main MacBook Pro, it's not booting, and now I want out. When I start my computer, it gives me the option to do an update or restart in safe mode. Either way, I get a loading bar for a bit before a grey screen of death. I've tried resetting the PRAM and Internet Recovery. I could previously get into single-user and verbose mode but after trying to fix the problem by enabling Trim (using these steps), but now when I boot I get a screen with a line through it. If I try to get back into single user or verbose mode, I get this plus a small error message that saying something like "Cannot find root user." I've also tried making a bootable Mavericks USB but trying to boot that (by holding C or the option key on startup), I get a dark blue screen. Question 1: is there any way I can get Mavericks back? Question 2: failing that, how would I wipe my HD and reinstall Mavericks?