Solution for MATROX parhelia cards
There have been a few posts about matrox drivers being a bit flakey. What I propose here is to tell you about how I fixed it. My 'puter is an HP DL580 (4x3.2g dualcore) 6G RAM etc.
So i told XFdrake that vesa was the driver and ran the installer from the matrox website (64bit). The trouble was it didn't write the correct stuff into xorg.conf.
After compiling the drivers and restarting X I found the best way to make matrox write the desired changes was to boot X and in a console run the file "mtxwizard". Following this I found the right stuff was finally written into xorg.conf and only a reboot was then required to load the kernel drivers and the correct X drivers subsequently.