look in the /etc/X11/XF86config or XF86config-4 depending on the distro he's using, and read the issues about configuring displays in /usr/share/doc/NVIDIA_GLX-1.0/nvidia-settings-user-guide.txt (if he installed the standard drivers downloaded from nvidia), so he can add/modify the corresponding lines, his problem is provably due to autodetection of the LCD screen and changing to CRT without reconfiguring for this kind of monitor
Hope it helps...
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