Reboot. As it passes POST, hold Left Shift. This should give you the grub boot menu. Hit E on the first entry, move to the end of the line starting with "kernel" or "linux" and add " S ". Then use the key it tells you to boot. (Ctrl - X maybe). This will boot you into single-user / recovery mode. If you get a command line successfully, then it's not a boot issue and is probably a graphics-related issue.
Also, please post hardware specs when asking a question, it saves time.