What to do if gems can't find ruby

From DevchixWiki

After you install Ruby, and run RubyGems for the first time, you may see this error:

C:\Ruby>cmd /k "C:\Ruby\bin\gem.bat"
'"ruby.exe"' is not recognized as an internal or external command,
operable program or batch file.

This means ruby isn't in the path. Desktop -> right click on My Computer -> select Properties -> Advanced tab -> Environment Variables button. Under System Variables, find Path, see if it has C:\Ruby\bin in it. If yes, reboot Windows so that all explorer processes get the updated path. If no, hit the edit button, and add C:\Ruby\bin; at the beginning.

Save and close. Close the RubyGems window and reopen it via the start menu. If Ruby is still not found, reboot the machine.