If NVIDIA is not finding screens for X

Things to check:
That you have BusID in your Device section - syntax example BusID "PCI:1:0:0" (you can discover it for example using nvidia-xconfig --query-gpu-info or pciconf -lv). If you have problem with finding modes for monitor you can add Option "ModeDebug" "True" to your Device section in xorg.conf.