Following update/upgrade with amd64 jessie, the 2 GTX 680 are seen by the graphical package VMD, however, "nvidia -smi" does not respond. The GTX are used in the absence of X-server, for number crunching.
I rerun upgrading at no help.
root@gig64:/home/francesco# dpkg -l | grep nvidia
ii glx-alternative-nvidia 0.5.1 amd64 allows the selection of NVIDIA as GLX provider
ii libegl1-nvidia:amd64 340.46-3 amd64 NVIDIA binary EGL libraries
ii libgl1-nvidia-glx:amd64 340.46-3 amd64 NVIDIA binary OpenGL libraries
ii libnvidia-compiler:amd64 340.46-3 amd64 NVIDIA runtime compiler library
ii libnvidia-eglcore:amd64 340.46-3 amd64 NVIDIA binary EGL core libraries
ii libnvidia-ml1:amd64 340.46-3 amd64 NVIDIA Management Library (NVML) runtime library
ii nvidia-alternative 340.46-3 amd64 allows the selection of NVIDIA as GLX provider
ii nvidia-cuda-dev 6.0.37-4 amd64 NVIDIA CUDA development files
ii nvidia-cuda-doc 6.0.37-4 all NVIDIA CUDA and OpenCL documentation
ii nvidia-cuda-gdb 6.0.37-4 amd64 NVIDIA CUDA Debugger (GDB)
ii nvidia-cuda-toolkit 6.0.37-4 amd64 NVIDIA CUDA development toolkit
ii nvidia-detect 340.46-3 amd64 NVIDIA GPU detection utility
ii nvidia-driver 340.46-3 amd64 NVIDIA metapackage
ii nvidia-installer-cleanup 20131102+2 amd64 cleanup after driver installation with the nvidia-installer
ii nvidia-kernel-common 20131102+2 amd64 NVIDIA binary kernel module support files
ii nvidia-kernel-dkms 340.46-3 amd64 NVIDIA binary kernel module DKMS source
ii nvidia-libopencl1:amd64 340.46-3 amd64 NVIDIA OpenCL ICD Loader library
ii nvidia-modprobe 340.46-1 amd64 utility to load NVIDIA kernel modules and create device nodes
ii nvidia-opencl-common 340.46-3 amd64 NVIDIA OpenCL driver
ii nvidia-opencl-dev:amd64 6.0.37-4 amd64 NVIDIA OpenCL development files
ii nvidia-opencl-icd:amd64 340.46-3 amd64 NVIDIA OpenCL installable client driver (ICD)
ii nvidia-profiler 6.0.37-4 amd64 NVIDIA Profiler for CUDA and OpenCL
ii nvidia-settings 340.46-2 amd64 tool for configuring the NVIDIA graphics driver
ii nvidia-smi 340.46-3 amd64 NVIDIA System Management Interface
ii nvidia-support 20131102+2 amd64 NVIDIA binary graphics driver support files
ii nvidia-vdpau-driver:amd64 340.46-3 amd64 Video Decode and Presentation API for Unix - NVIDIA driver
ii nvidia-visual-profiler 6.0.37-4 amd64 NVIDIA Visual Profiler for CUDA and OpenCL
ii nvidia-xconfig 340.46-1 amd64 X configuration tool for non-free NVIDIA drivers
ii xserver-xorg-video-nvidia 340.46-3 amd64 NVIDIA binary Xorg driver
root@gig64:/home/francesco#
I can't remember which nvidia driver was operating before these problems.