Please delete/comment from your xorg.conf from Section "Screen" following lines:
SubSection "Display" Modes "1024x768" "800x600" Virtual 640 480 EndSubSection
and try if this helps.
Then remove from your xorg.conf from Section "Monitor" following lines:
HorizSync 30.0 - 71.0 VertRefresh 50.0 - 90.0
and try if the monitor settings will be detected automaticly.
Please delete/comment from your xorg.conf from Section "Screen" following lines:
SubSection "Display"
Modes "1024x768" "800x600"
Virtual 640 480
EndSubSection
and try if this helps.
Then remove from your xorg.conf from Section "Monitor" following lines:
HorizSync 30.0 - 71.0
VertRefresh 50.0 - 90.0
and try if the monitor settings will be detected automaticly.