nvidia binary driver not used even though enabled in "Additional Drivers"

[JG]

In "Software & Updates" the recommended NVIDIA binary driver - version 331.38 (proprietary, tested) is selected. Furthermore the dialog displays "1 proprietary driver in use" (see screenshot).
Nevertheless, running `lshw -c video` shows that (after several reboots) nouveau is still used:
 *-display
       description: VGA compatible controller
       product: GT218M [NVS 3100M]
       vendor: NVIDIA Corporation
       physical id: 0
       bus info: pci@0000:01:00.0
       version: a2
       width: 64 bits
       clock: 33MHz
       capabilities: pm msi pciexpress vga_controller bus_master cap_list rom
       configuration: driver=nouveau latency=0
       resources: irq:42 memory:cc000000-ccffffff memory:d0000000-dfffffff memory:ce000000-cfffffff ioport:2000(size=128) memory:cd000000-cd07ffff

As another symptom running "nvidia-settings" does not display any devices.

Everything worked fine when enabeling the proprietary driver the first time. I then reverted back to nouveau and then tried to enable the NVIDIA driver again. Since then the problems started. Purging and re-installing the NVIDIA packages did not help.

[Sylvain Rabot (sylr)]

I have the exact same problem :

rabosy@isis:~$ sudo lspci -s 03:00.0 -v
03:00.0 VGA compatible controller: NVIDIA Corporation GK104 [GeForce GTX 760] (rev a1) (prog-if 00 [VGA controller])
 Subsystem: Micro-Star International Co., Ltd. [MSI] Device 2847
 Flags: bus master, fast devsel, latency 0, IRQ 82
 Memory at ee000000 (32-bit, non-prefetchable) [size=16M]
 Memory at f0000000 (64-bit, prefetchable) [size=128M]
 Memory at f8000000 (64-bit, prefetchable) [size=32M]
 I/O ports at d000 [size=128]
 Expansion ROM at ef000000 [disabled] [size=512K]
 Capabilities: [60] Power Management version 3
 Capabilities: [68] MSI: Enable+ Count=1/1 Maskable- 64bit+
 Capabilities: [78] Express Endpoint, MSI 00
 Capabilities: [b4] Vendor Specific Information: Len=14 <?>
 Capabilities: [100] Virtual Channel
 Capabilities: [128] Power Budgeting <?>
 Capabilities: [600] Vendor Specific Information: ID=0001 Rev=1 Len=024 <?>
 Capabilities: [900] #19
 Kernel driver in use: nouveau

rabosy@isis:~$ dpkg -l | grep nvidia
ii nvidia-340 340.29-0ubuntu1 amd64 NVIDIA binary driver - version 340.29
ii nvidia-libopencl1-340 340.29-0ubuntu1 amd64 NVIDIA OpenCL Driver and ICD Loader library
ii nvidia-opencl-icd-340 340.29-0ubuntu1 amd64 NVIDIA OpenCL ICD
ii nvidia-prime 0.6.2 amd64 Tools to enable NVIDIA's Prime
ii nvidia-settings 340.29-0ubuntu1 amd64 Tool for configuring the NVIDIA graphics driver

rabosy@isis:~$ sudo modprobe nvidia_340
modprobe: ERROR: could not insert 'nvidia_340': No such device