Windows 10, 64 bits, Geforce GTX 1080
Short description of error
Blender User Prefernces -> System -> Cycles Compute Device
shows "None". No CUDA devices can be selected.
Exact steps for others to reproduce the error
Install the latest Nvidia 378.66 drivers and Blender 2.78b
To solve the problem:
Roll back to Nvidia 376.33 driver. Problem caused by the Nvidia´s latest driver.
Reason that I report the problem here might be that the information might be useful to Blender developers also?