im quite off linux but u can always google that
ok so did some research for u and a user with a similar type of prob. tried this
u can even try this
. Used the command line tool "xrandr --output TMDS-1 --mode 1920x1200" to change current screen resolution.
--> In current session 1920x1200 available.
15. Detected inappropriate monitor modes in current xorg.conf, version yxz. Corrected them.
--> Reboot, and ... unexpectedly ... the 1920x1200 was there, Heureka !
16. From now on I was eager to find the configutration that didn't work, just in order to spot the problem and its cure. First I peplaced xorg.conf with that of step 10.
--> Reboot, 1920x1200 still ok.
17. Undo all disactivations in rc2.d
--> Reboot, 1920x1200 still ok.
18. Used original ubuntu 8.04 xorg.conf, that is almost empty with respect to graphics and monitor. (xorg_orig_8.04.conf)
--> Reboot, 1920x1200 still ok.