A desktop user needed a PCI-Express dual video card installed for his Optiplex 320 computer. After trying several types of dual-port video cards the drivers and programs for those video cards were uninstalled from the Windows XP operating system using 'Add/Remove Programs' via the Control Panel. Afterwards the computer was rebooted and the screen of the Samsung LCD monitor (which is now connected to the computer's on-board VGA port) just blacks out along with an error message saying "Not Optimum mode Recommended mode: 1280x1024 60Hz". Attempted to restart the computer in "SAFE" mode to fix the issue the screen blacks out again with the same error message.
To fix this issue boot the computer into "VGA" mode (NOTE: Typically hitting the F8 key during the computer's bootup sequence will invoke the option to enter VGA mode) and lower the display resolution less than the LCD's maximum resolution mode. After the display resolution has been lowered in "VGA" mode then reboot the computer and enter into "Normal" mode. While in "Normal" mode set the correct native resolution of your computer to work below the LCD's maximum resolution and all should be fine.
Optional - Up until this point the issue should be resolved however after uninstalling the drivers and programs for the dual video cards it apparently affected/corrupted the graphics driver for the onboard video card (e.g. ATI Radeon Express 1100) on this computer. The graphics driver for the ATI Radeon Express 1100 was downloaded and reinstalled for the native (on-board) graphics driver(s). Afterware the computer was rebooted and the everything was working fine.