ruby and rails wont work even they're already installed

mongskie@mongskie-os:~$ gem
/usr/bin/gem:4: undefined method `manage_gems' for Gem:Module
(NoMethodError)

mongskie@mongskie-os:~$ rails
/usr/lib/ruby/1.8/active_support/dependencies.rb:55: uninitialized
constant ActiveSupport::Dependencies::Mutex (NameError)
  from /usr/local/lib/site_ruby/1.8/rubygems/custom_require.rb:36:in
`gem_original_require'
  from /usr/local/lib/site_ruby/1.8/rubygems/custom_require.rb:36:in
`require'
  from /usr/lib/ruby/1.8/active_support.rb:56
  from /usr/share/rails-ruby1.8/railties/bin/../lib/rails_generator.rb:
28:in `require'
  from /usr/share/rails-ruby1.8/railties/bin/../lib/rails_generator.rb:
28
  from /usr/share/rails-ruby1.8/railties/bin/rails:14:in `require'
  from /usr/share/rails-ruby1.8/railties/bin/rails:14

I always get these messages. Why is this. Pls help me.

I can only advise you to use rvm (type this in Google ) and update your Ruby and rails to newest version.

If you can’t update Rails or downgrade RubyGems, you need to require ‘thread’ before boot.rb runs, in three files: Rakefile, script/server, and config/environment.rb. It seems older versions of Rails relied on a require from
RubyGems, giving us that delightful error message upon updating RubyGems to a newer version, which does not require thread.rb by default. More info:
http://stackoverflow.com/questions/5176782/uninitialized-constant-activesupportdependenciesmutex-nameerror

[]s,

Paulo