After a fresh install of ruby for Windows 64x, I was able to install gems with no problem, but the "ruby" command itself is not recognized, which I need to setup ruby devs and install jekyll.
EDIT:
In case someone else is in my situation, the thing that finally worked for me was to uninstall ruby and make a clean installation with the 2.2.6 version of the installer (https://rubyinstaller.org/downloads/). Then I was able to install Sass, Ruby devKit and Jekyll. The executable of Ruby 2.4.3 just won't work.
It sounds like Ruby is not in the path.
Try specifying the full path to the Ruby Executable.
"C:\Your\Path\To\Ruby\Install\Ruby.exe"
assuming that works edit the path variable to add Ruby's path:
Path %PATH%;C:\Your\Path\To\Ruby\Install
That will then allow Ruby to run directly by just typing the executable's name.