Grunt not working

grunt server --force is not working and throughing below errors.

c:/Ruby200-x64/lib/ruby/2.0.0/rubygems/dependency.rb:296:in `to_specs': Could no
t find 'grunt' (>= 0) among 24 total gem(s) (Gem::LoadError)
        from c:/Ruby200-x64/lib/ruby/2.0.0/rubygems/dependency.rb:307:in `to_spe
c'
        from c:/Ruby200-x64/lib/ruby/2.0.0/rubygems/core_ext/kernel_gem.rb:47:in
 `gem'
        from c:/Ruby200-x64/bin/grunt:22:in `<main>'

Problem caused after restarting the PC. I have tried below commands.

gem uninstall grunt
npm install -g grunt-cli
npm install

I am using window-8 OS.