Haha..
Like a moron I went and did precisely what the OP warned not to — checked the box to turn off read access to all admins. Unbootable is right 🙂 no last known good config or safe mode either. Luckily I had another bootable partition on the drive…got a little education in restoring registry hive files. Careful with those registry permissions, kids. But actually following the instructions, it does work, so thanks!
