A black screen is usually either a mismatch between your video HW and the XFree86 configuration, or a video card miconfigured for the monitor.
What kind of video card? What kind of monitor?
The various ways to configure, startup, and debug X11 have evolved over the years. This might help:
http://en.tldp.org/HOWTO/XFree86-HOWTO/
Try to find the log created by XFree86 (rh9: /var/log/XFree86.0.log) and look for any errors.
Try to find your XF86Config file (rh9: /etc/X11/XF86Config) and examine the settings and compare that to your video card.
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Qneill