Another thing you can try is, check in advance settings of screen resolution (right click on desktop, etc.) that the monitor option "hide modes monitor doesn't support" is deactivated, perhaps you's resolution will appear. ". Also, if you're using the digital cable for the screen, change it to the analog cable, you might have a different choice of resolutions.
In the end, you might want to try Win Vista 64 (with Service Pack 2 its a W7 perfomance wise, it has even dx11).