Another thing to check is /etc/X11/xorg.conf under the section "ServerFlags" to see if the option "AutoAddDevices" is set to "False". I've included my xorg file for reference - see the last line.
John
# nvidia-xconfig: X configuration file generated by nvidia-xconfig
# nvidia-xconfig: version 1.0 (buildmeister@builder75) Fri Mar 12 01:42:27 PST 2010
Section "ServerLayout"
Identifier "Layout0"
Screen 0 "Screen0"
InputDevice "Keyboard0" "CoreKeyboard"
InputDevice "Mouse0" "CorePointer"
EndSection
Section "Files"
EndSection
Section "InputDevice"
# generated from default
Identifier "Mouse0"
Driver "mouse"
Option "Protocol" "auto"
Option "Device" "/dev/psaux"
Option "Emulate3Buttons" "no"
Option "ZAxisMapping" "4 5"
EndSection
Section "InputDevice"
# generated from default
Identifier "Keyboard0"
Driver "kbd"
EndSection
Section "Monitor"
Identifier "Monitor0"
VendorName "Unknown"
ModelName "Unknown"
Option "DPMS"
# ModeLine "1024x768" 65.00 1024 1048 1184 1344 768 771 777 806 -hsync -vsync
ModeLine "1024x768_75.00" 78.75 1024 1040 1136 1312 768 769 772 800 -hsync -vsync
HorizSync 20-500
VertRefresh 74-76
EndSection
Section "Device"
Identifier "Device0"
Driver "nvidia"
VendorName "NVIDIA Corporation"
Option "XvmcUsesTextures" "true"
Option "renderAccel" "true"
Option "UseEDID" "true"
Option "ExactModeTimingsDVI" "true"
Option "NoLogo" "true"
Option "NoBandWidthTest" "true"
Option "ModeValidation" "NoDFPNativeResolutionCheck, NoEdidMaxPClkCheck, NoMaxPClkCheck, AllowInterlacedModes, AllowNon60HzDFPModes, NoEdidModes"
Option "DynamicTwinView" "false"
Option "UseEvents" "true"
Option "AllowGLXWithComposite" "true"
Option "AddARGBGLXVisuals" "true"
Option "ConnectedMonitor" "DFP"
EndSection
Section "Screen"
Identifier "Screen0"
Device "Device0"
Monitor "Monitor0"
DefaultDepth 24
SubSection "Display"
Modes "1024x768_75"
EndSubSection
SubSection "Device"
Modes "1024x768_75"
EndSubSection
EndSection
Section "ServerFlags"
Option "AutoAddDevices" "False"
EndSection