Whenever posting questions on these forums, please give us as much information as possible about your computer. Depending on your issue, we might need the operating system, processor speed, amount of RAM installed, brand name of the computer, (if there is one), and any EXACT error messages you are receiving, and any other info you think might be helpful. The more information you give us, the better informed our answer will be.
In the meantime, I would start by visiting the manufacturer's website and downloading, then installing an updated graphics/display driver. You can find the "display driver" manufacturer and version number in the "Device Manager" section of the computer or, if your computer is a brand name model, then visiting the computer manufacturer's site and checking for drivers for your particular machine should allow you to find the most recent driver.
You might also be setting the resolution at a setting which is higher than the video card can handle. Will the resolution "stick" if you keep it at 800 x 600?
Hope this helps.
Why does my resolution change during start up? On my home computer, I only have to change it once. On my laptop-- it keeps changing every few seconds--HELP !!