I agree that the init level in inittab has nothing to do with this. Don't waste your time with it. The issue is not the init level--it's the failure of the GUI to start.
I would suggest this as another possible test, in addition to the other excellent suggestions you've gotten:
After logging in at the command line and before running startx, run xwmconfig as user and change your default window manager to something other than KDE. I would suggest Fluxbox or Blackbox or one of the other lightweight window managers.
Run startx and see if the GUI starts.
If it does, it indicates that the problem is something to do with KDE specifically. If it doesn't, you have a larger issue.
Note any error messages that come to the screen when you run startx (you may want to take a digital picture for convenience--if you do, turn off the flash and, if possible, set the camera to "S" or "shutter-priority" mode).
You could also log directly into the box as root (Slackware allows that) and try startx to test whether the GUI starts correctly.
Last edited by frankbell; 11-21-2012 at 10:05 PM.