i can share you my solution here,hope it may works
pik list
It should show you
187: ruby 1.8.7 (2010-08-16 patchlevel 302) [i386-mingw32] 192: ruby 1.9.2p290 (2011-07-09) [i386-mingw32] 193: ruby 1.9.3p327 (2012-11-10) [i386-mingw32]
200: ruby 2.0.0p247 (2013-06-27) [i386-mingw32] If its not pointing to ruby version 200 then
pik use 200
ruby dk.rb install It will enhance DevKit to your installed Rubies
Finally gem install rails
This will install latest rails version 4 for Ruby 2.0