Welcome the board, Khouri.
Can you tell us when and how the problem began? Are you trying to change colors from 16bit (normal high resolution) or 16 (low) to 256?
I take it you can access Display Properties, just not the settings tab?
You may need to remove and reinstall or change your current video drivers to correct this. Do you know what you have?
It would be useful to know whether the error occurs when trying to access the settings tab in safe mode.
To start in safe mode, press and hold the ctrl key as soon as the computer starts up. You will see a boot menu with the safe mode option. Once safe mode is loaded, access Display Properties (you can right click the desktop and select properties). Test the Settings tab. If it opens without error also click the Advanced and Adapter tabs and see what it says for your current adapter.
You won't be able to make any settings changes in safe mode (although you coulld instruct Windows to search for another adapter). This is just for test purposes.