did you try the other F keys? like F2 f3 ...
if you get to grub you can try booting into older kernel versions or edit the grub start command with the "e" key and turn on verbose (shut off quiet) and see if you can see your problem.
I just tried to boot up my ubuntu machine and got two error messages. The first one said, "failed to load modual 'i810'" and the second one said, "config/hal: couldn't initialize context: unknown error".
I tried to hit ctrl+alt+f1 and try to update my graphics driver (thought it might help) but it didnt even give me a login prompt.