Welcome to SevenForums: I noticed you didn't list your display in your system specs.
If in device manager it's listed as PNP you might want to check the manufacturers site and see if their is a driver
(.inf file) for your display and install it.
Once device manager recognizes your display for what model it is usually you'll be able to have access to it's native resolution.
You might also want to check in Nvidia control panel and see if you can change the resolution manually. Control panel>nvidia control panel>change resolution tab> see what it lists as available if your current 600x800 is the only one you can try and create a custom resolution but you'll need to know what your displays native resolution is as well as what hertz it runs at, if an LCD usually it's 60 hrz.
I have found that this problem is usually corrected once the display is recognized properly in device manager which would require it's driver to be installed. If you would provide the make and model # we could see if one is available. Thanks. Fabe