grub debugging

In the grub menu, type e to edit the default entry, and append debug at the end of the line that says quiet. In fact, removing quiet is fine.

Open Another window

Try hitting ctrl+alt+F1 that should take you to the terminal with a login prompt.

Ubuntu and Nvidia

Try and put this on the boot line


Fast Boot

One more point: In addition to the EFI's fast boot option, there's an option in Windows called Fast Startup, and another called Hibernate. These MUST both be disabled if you're to safely dual-boot.

Boot options