NVIDIA 343 driver and GTS 250

Problem

On a computer with a NVIDIA GeForce GTS 250 graphics card running Ubuntu 14.04, I decided to update the installed driver from nvidia-331 to nvidia-343. I did this:

$ sudo apt-get install nvidia-343

It installed the driver and then compiled and installed the kernel module. I rebooted the computer. I was able to login in the GUI, but got an empty desktop!

Solution

What kind of graphics driver problem allows graphics, but only hides the desktop elements in Unity? No idea. I dug through /var/syslog, searched for nvidia and found this:

NVRM: The NVIDIA GeForce GTS 250 GPU installed in this system is
NVRM:  supported through the NVIDIA 340.xx Legacy drivers. Please
NVRM:  visit http://www.nvidia.com/object/unix.html for more
NVRM:  information.  The 343.22 NVIDIA driver will ignore
NVRM:  this GPU.  Continuing probe...
NVRM: ignoring the legacy GPU 0000:03:00.0

So, it turns out that the GTS 250 is no longer supported in the 343 version drivers and later. I removed this driver and reinstalled back 331 driver and got back my desktop.