If you can get back to a command line, use the xorgconfig command to set up your X.
(as Root) # xorgconfig
Before you do that, you might just want to type at the command line:
You should get some output like this:
X: /usr/bin/X /usr/X11R6/bin/X /usr/bin/X11/X
If not, then you probably don't have the X Windows System part of Slack installed.