Try putting the following in /etc/X11/xorg.conf.d under the name "02-screen.conf"
Section "Default Screen Section"
Viewport 0 0
I hope the Identifier, Device, and Monitor lines have the default names used as I don't know for sure what they should be. The names I give above are from a generic run of "Xorg -configure" which will generate a mostly valid configuration based on the hardware installed. I say mostly, because it cannot tell at configure time whether the monitors attached are actually valid - so if a videocard supports multiple (my card has three, but only two have plugs, and of those two, only one is used), it will define multiple, which will cause errors when it tries to actually use that configuration.
The Subsection "Display" specify the number of bits to use and the display specifies the resolution (the Modes line). There can be multiple modes, which should allow you to cycle through the list (ctrl-alt-+ or ctrl-alt-- (the +/- last character is from the keypad)). You can find valid modes to list in your /var/log/Xorg.0.log files identified by lines with "Modeline" followed by the mode name, and a list of timing numbers associated with that specific mode.
And if all else fails, delete the file (sorry about that).
Oh - forgot. You will have to log out before it will take effect. Just be sure you can login through a console virtual terminal (ctrl-alt-F2/3/...) to delete the file. If it doesn't work, the X display will not start...