Ubuntu – Tried every solution but the monitor resolution is still stuck at 640×480

I have problems getting my Viewsonic VX2025wm LCD monitor with Ubuntu 11.10. I have another monitor which works well (although in VGA mode), but this one refuses to go beyond 640×480. I'm trying to set it at 1680×1050 (60Hz). I'm using the latest NVIDIA drivers on a Geforce GTX 560 TI.

I tried using xrandr using this solution: http://www.linuxjournal.com/content/guerrilla-tactics-force-screen-mode-ubuntu but I get the following error:

Failed to get size of gamma for output default

If I list the available modes, none are higher than 640×480.

I tried a few solutions proposed here: Monitor will not be detected, stuck at 640×480

Forcing the resolution in xorg.conf doesn't work, but the monitor always falls back to 640×480.

I also tried using nvidia-xconfig –mode=1680×1050 but it doesn't work either.

I tried deleting my xorg.conf file, but the monitor still falls back to 640×480.

This guy has the exact same monitor as me but a slightly different problem (he can set it higher than 640×480, but not 1680×1050): Getting screen resolution correct with nvidia drivers

Here is my current xorg.conf:

# nvidia-xconfig: X configuration file generated by nvidia-xconfig
# nvidia-xconfig:  version 295.20  (buildmeister@swio-display-x86-rhel47-05.nvidia.com)  Mon Feb  6 22:13:40 PST 2012

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"
    HorizSync       28.0 - 33.0
    VertRefresh     43.0 - 72.0
    Option         "DPMS"
EndSection

Section "Device"
    Identifier     "Device0"
    Driver         "nvidia"
    VendorName     "NVIDIA Corporation"
EndSection

Section "Screen"
    Identifier     "Screen0"
    Device         "Device0"
    Monitor        "Monitor0"
    DefaultDepth    24
    SubSection     "Display"
        Depth       24
        Modes      "1680x1050"
    EndSubSection
EndSection

FYI, the monitor has always worked without any problem with any version of Windows. I'm not saying Windows works better, I'm just saying the monitor works normally with another OS.

Thanks for any help. I'm really going crazy here!