If you have an Intel 915 chip set or above, install the 915 resolution package. Or if you have on board video, you may not have enough memory allocated to support 'depth 24', if your /etc/xorg.conf has a default depth of 24, try changing it to 16. If all else fails, you can go through a step by step re-configuration to include proper monitor sync rates and refresh rates. Get a hold of the specs for the monitor from manufacturer on-line and start configuration from command line with this command:
Code:
system-config-display --reconfigure
There will also be a step for setting default resolution.