When you run startx and nothing happens, the error is written into the log file of the X windows usually located at /var/log/Xorg.0.log. Errors are usually marked with "(EE)". You can extract information Error in Xorg.0.log with this command
# grep EE /var/log/Xorg.0.log
If you do not have a xorg.conf file, you can install by running
# yum install system-config-display
# system-config-display
If system-config-display setup GUI is not able to solve the issue, you can use command line
# system-config-display --set-resolution=1280x960 --set-depth=32 --set-driver=nvida (For more options, run system-config-display --help)
