Same thing happening to me… Just made the switch over from FCE about 2 weeks ago. Running into a number of weird issues including screen digitizing into nonsense, timelines not showing up, and now it won’t even boot. I pulled my external drives, try removing project files, to no avail. On the phone with Apple support now (or should I say, on hold…). I’ve spent about 30 hours in the software and was really starting to like it… man.