So I installed the beta last Sunday and had zero issues until Thursday, when my Mac started running into bootup issues. I've experienced the following scenarios: Computer won't boot at all. I've attempted SMC resets multiple times, the "hold the power button for ten seconds and then press the button again" method, and still I only get it to boot up maybe once every ten attempts. When it does boot, there's no startup chime, so I usually miss my cue to hit cmd-r or the shift key (I've yet to successfully boot into Safe Mode) I've attempting booting into Internet Recovery mode twice now, and each time it fails (the initial progress bar fills, and as soon as it gets to the gray screen with the Apple logo it crashes). When I miss my chance at booting into an alternate mode, it takes me to the regular log in screen, where I enter my password. On three occasions (out of at least a dozen at this point, probably closer to 20) it managed to log in successfully; it never lasts long before it crashes and I'm stuck with a black screen yet again. When I hit the 'restart' button on the login screen it shuts off but won't turn back on. I have a Genius appointment on Monday but I'd like to resolve this sooner rather than later. Thoughts, suggestions (in the meantime I'll be continuing to attempt booting into Safe Mode)? EDIT: I've basically reached the conclusion that either I'm not hitting "Shift" quickly enough or my Mac just doesn't want to boot into Safe Mode. EDIT2: Got the startup chime, held down the shift key—nothing. Nada.