Check /var/tmp/Xorg.0.log. Look for the resolutions supported by your monitor. If 1280x1024 is indeed supported by your monitor, then there's probably an error saying why. Also check out /etc/X11/xorg.conf and see what resolutions are under
I have
Code:
SubSection "Display"
Viewport 0 0
Depth 8
Modes "1280x1024" "1024x768" "800x600" "640x480"
EndSubSection