The xpdyinfo is just to confirm that extensions such as GLX and NVIDIA-GLX are enabled.
The only other possibility is that your x-server misdetected the default settings for your monitor and now you only have a bunch of non-standard resolutions available.
What the server does is tries to detect the physical dimensions of your monitor and then calculates the available screen resolutions based on your DPI. What can happen if this is messed up, is you'll get your standard desktop resolution, and a lot of weird ones like 640x350.
Generally you'll be able to tell if this is a problem by using the KDE or Gnome Controls to change the desktop resolution.
The only other possibility is that your x-server misdetected the default settings for your monitor and now you only have a bunch of non-standard resolutions available.
What the server does is tries to detect the physical dimensions of your monitor and then calculates the available screen resolutions based on your DPI. What can happen if this is messed up, is you'll get your standard desktop resolution, and a lot of weird ones like 640x350.
Generally you'll be able to tell if this is a problem by using the KDE or Gnome Controls to change the desktop resolution.