Running docker info
from an elevated PowerShell prompt shows this error:
error during connect: Get http://%2F%2F.%2Fpipe%2Fdocker_engine/v1.2
I had the same issue in windows 7. I found my issue was getting the VM working in virtual box.
Copy the "Boot2Docker.iso" file from "C:\Program Files\Docker Toolbox"
into "C:\Users\\.docker\machine\cache"
Then I could run the start.sh in cygwin or Gitbash.
Note: I had to restart any cmd's for the docker to see the VM.