Linux - Where should I start when diagnosing display problems?
One of the most useful tools for diagnosing problems is the X
log file in /var/log (the file is named: "/var/log/XFree86.<#>.log" or
"/var/log/Xorg.<#>.log" where "<#>" is the server number -- usually 0).
Lines that begin with "(II)" are information, "(WW)" are warnings, and
"(EE)" are errors. You should make sure that the correct config file
(ie the config file you are editing) is being used; look for the line
that begins with: "(==) Using config file:". Also check that the
NVIDIA driver is being used, rather than the 'nv' or 'vesa' driver;
you can look for: "(II) LoadModule: "nvidia"", and lines from the
driver should begin with: "(II) NVIDIA(0)".