Ahh, great-when-installed-but-buggy-installer ol' Ark Linux.
Problem is, it's in alpha and it's a great distro, but its installer.... well, it kinda sucks (especially in alpha 10).
When GRUB loads up, you should hilight the Ark entry, and hit `a' -- add a `3' to whatever line is there and then hit <enter> -- when presented with a login screen, login as `arklinux' and then type in `su' to become root (no password needed) -- type `X -configure' (it's pretty self explanatory) -- it willl generate a config file at /foo/bar (it will tell you) -- type `XFree86 -xf86config /foo/bar/XF86Config' and see if a black screen with an X cursor appears. If so, do ctrl+alt+backspace to take you back to the shell.
Reboot, without touching anything, and your machine should boot properly.
Alternatively, you could wait a day or two for alpha 11 to come out, which will probably fix that common bug of alpha 10.
if you need any more help, visit the official forum at www.arklinux.info/ark.mb