FC16: can't log in via LightDM or GDM (but 'startx' works fine)

Question

I'm running Fedora Core 16 (with all patches applied as of 11 Feb 2013, AFAICT) on a dual-monitor Lenovo workstation, and can't seem to access my desktop via a graphical login manager. My system boots normally, I get the GDM greeter screen, I select my username and enter my password, and log in. I then get a black screen like Xorg is trying to switch modes before being sent back to the GDM login screen. The same problem happens when I removed GDM and attempted to use LightDM instead.

However, if I boot into runlevel 3, log in via the console, and run 'startx', my GNOME desktop appears normally.

Running tail /var/log/Xorg.0.old tells me that my previous Xorg session (the one launched from GDM) terminated normally:

[  1125.791] (II) NVIDIA(GPU-0): --- End of ModePool for Lenovo Group Limited LEN LT2452pwC (DFP-1): ---
[  1125.791] (II) NVIDIA(GPU-0):
[  1175.892] (II) evdev: Dell Dell USB Keyboard: Close
[  1175.892] (II) UnloadModule: "evdev"
[  1175.892] (II) Unloading evdev
[  1175.892] (II) evdev: Microsoft Microsoft 3-Button Mouse with IntelliEye(TM): Close
[  1175.892] (II) UnloadModule: "evdev"
[  1175.892] (II) Unloading evdev
[  1175.892] (II) evdev: Power Button: Close
[  1175.892] (II) UnloadModule: "evdev"
[  1175.892] (II) Unloading evdev
[  1175.892] (II) evdev: Power Button: Close
[  1175.892] (II) UnloadModule: "evdev"
[  1175.892] (II) Unloading evdev
[  1175.921] Server terminated successfully (0). Closing log file.

What's going on? What logs can I examine for more information?

Answer 1

I guess something is wrong with your xorg.conf file since the log file mentions DFP-1
the first DFP should be DFP-0
Have you tried using an external monitor or editing the xorg.conf?

EDIT:
Have you checked permissions for root(/), /home and $home (/home/[your name])?