That happened to me a while ago on a different distro. It turned out that one of the service was failing, so startup never actually completed. That is, one of the executable scripts in /etc/init.d/ would fail and hang. The X server worked, so it wasn't totally obvious there was a problem.
I tracked it down by closely watching the screen during boot to see that last thing displayed before X took over, looking at the logs in /var/log/, and disabling services one by one until startup completed.