I don't know what that error is but have you tried starting X as root to see if you have a permissions problem.
Have you run xf86config or xorgconfig again to reconfigure X differently. Like lowering the resolution or bits per pixel.
When X starts then kicks you back to shell I would think it is a X config problem. Unless you have something missing from X.
Here's a full version of Slack.
http://linuxiso.org/distro.php?distro=17