On Tue, 2005-11-22 at 16:40 +0000, Mark Nelson wrote:
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> Hello
> 
> I have a couple of AMD 64 machines running SL4.0 in 32bit mode, the
> graphics card is a Matrox Graphics, Inc. MGA G550 AGP.  The problem I
> have is that I cannot get the graphics card to display above 1024x768
> either a NEC or a Samsung Monitor (both these monitors are capable of
> supporting 1280x1024). I'm running xorg-x11-6.8.1-23.EL

Check /var/log/Xorg.0.log for messages about not using certain modes (..
out of range),  and the DDC output for the frequency ranges supported by
your monitor:
e.g.
(II) I810(0): Ranges: V min: 50  V max: 75 Hz, H min: 24  H max: 80 kHz, PixClock max 140 MHz
...
Then compare to your /etc/X11/xorg.conf "Monitor" section to make sure
you are not constraining the frequency ranges there with respect to what
your monitor will support.

See
http://wiki.x.org/wiki/FAQVideoModes#head-8891acdd12af18ef2c26fd86e50c194ac26eb0f
for examples of the log and matching config file.

Regards
jan