Try updating the driver for your video card. In most cases, when you're attempting to use other resolutions and it's not possible, it's often an indication that the driver is outdated. You can get that from the video card or computer manufacturer's website.
There may be some misunderstandings here... but here goes! The monitor is a SyncMaster 2333HD (Analog), attached to an HP running WinXP SP3. We would like to use the whole screen, so we have it set to 16:9. The screen display settings are currently 1280 x 768, so there is an annoying distortion of any images. I saw where 1920 x 1080 is recommended, but that makes the text way too small for legibility! I am told that 1280 x 720 would give the right proportions, but that is not given as an option on my list of possible settings (under WinXP). What can I change to fix this problem - either on the PC or on the monitor?