Did you put the proper values for your monitor in the xorg.conf? If you do not have the manual for the monitor then use a Google search with the make/model number to get the proper values. Here is what a monitor section looks like with the values used in case there is none in yours and if you cannot get it going can you post your xorg.conf and the /var/log/Xorg.0.log files.
Code:
# NEC P1250 +
Section "Monitor"
Identifier "Monitor0"
VendorName "NEC"
ModelName "P1250 +"
HorizSync 31-110
VertRefresh 55-160
Option "DPMS" "true"
EndSection