I have installed fedora 6 on DELL optilex 330 series, I am not getting GUI,I am getting command mode login. After login I have typed "starx" , I am getting error like this.

Fatal Server error:
Server is already active for display 0
If this server is no longer running, remove /tmp/.X0-lock and start
agian

xlib :connection to ":0.0" refused by server
xlib :Invalid MIT - MAGIC - 1 KEY giving up
xinit: unable to connect to x server
xinit: No such process (errno 3) Server error

I believe I use Optiplex 330's at school. And they run Ubuntu just fine, in fact I think they run Fedora 6.
What I would do is try and reinstall Fedora. What may be the issue is the graphics drivers not being available, otherwise it is possibly a corrupt install.
Also, if you try a more recent distribution, it may actually fix the problem. For example, Ubuntu 8.10.

It is really weird. I tried everything but still this is what I get, when I run 'startx'

xauth: creating new authority file /root/.serverauth.3385

X Window System Version 7.1.1
Release Date: 12 May 2006
X Protocol Version 11, Revision 0, Release 7.1.1
Build Operating System: Linux 2.6.9-55.ELsmp i686 Red Hat, Inc.
Current Operating System: Linux xxxxxx---xxxx 2.6.22.14-72.fc6 #1 SMP Wed Nov 21 15:12:59 EST 2007 i686
Build Date: 18 June 2007
Build ID: xorg-x11-server 1.1.1-47.10.fc6
Before reporting problems, check ....xxxx....
to make sure that you have the latest version.
Module Loader present
Markers: (--) probed, (**) from config file, (==) default setting,
(++) from command line, (!!) notice, (II) informational,
(WW) warning, (EE) error, (NI) not implemented, (??) unknown.
(==) Log file: "/var/log/Xorg.0.log", Time: Thu Jan 8 10:49:36 2009
(==) Using config file: "/etc/X11/xorg.conf"
(EE) No devices detected.

Fatal server error:
no screens found
XIO: fatal IO error 104 (Connection reset by peer) on X server ":0.0"
after 0 requests (0 known processed) with 0 events remaining.


any idea?

Try using a newer distribution e.g. Fedora 10. Fedora 6 is no longer supported by the Fedora Project.