I've got a one week old Sony Vaio laptop with Win8 that started failing on login. The first symptom seems to have been Firefox failing to load any image files - just raw text. I believe that began right after a reboot. The next attempt to boot failed after the password screen, leaving me with nothing but a mouse cursor and blackness. Lots of blackness.
Running the Vaio troubleshooting wizard hasn't helped, although there is the nuclear option of reinstalling - which I'd prefer to leave as my last choice once all other possibilities are exhausted.
Starting in Safe Mode led to the same black screen and restoring a previous system mount point from the command prompt (rstrui.exe) didn't appear to help either.
One more element to make this even more fun: this all happened in the midst of a successful attempt to add a UEFI Ubuntu Linux dual-boot option. The Ubuntu partition is booting perfectly.
Anyone have any ideas?