While trying to validate the installation of tensorflow-gpu, I get an ImportError when trying to execute \"import tensorflow as tf\". I am using a Quadro K620 on Windows 7.
I came across the same issue today, please switch to cuDNN v5.1 Library for Windows instead as @mickdelaney suggested and then try to
Check environment settings of CUDA, normally all the settings of CUDA had been added to Windows environment
Copy files in bin, lib and include of cuDNN to bin, lib and include of CUDA respectively. Normally the directory is C:\Program Files\NVIDIA GPU Computing Toolkit\CUDA
And then you can import tensorflow and run your code. Good luck!