Yeah, see all those "horizontal refresh out of range" warnings there. Try what Yamaneko said, with your refresh rate. You'd have to look it up in your monitor's documentation. I've had problems with screen resolution too when the refresh rate was wrong or not specified in xorg.conf. If worse comes to worse you may have to google for a modeline for your monitor, even. To get my widescreen monitor to work at 1680x1050 it took me forever to get the right modeline.