Cannot install Ruby's sass gem

Question

I am trying to install ruby' gem sass. I have run Ruby installation first and: gem install sass. But I am getting an error:

C:\Windows\system32>gem install sass ERROR: Could not find a valid gem 'sass' (>= 0) in any repository

Any idea what that might be?

Thanks

Update.
The connad: gem sources --add https://rubygems.org/ fails:
C:\Windows\system32>gem sources --add https://rubygems.org/
Error fetching https://rubygems.org/:
Errno::ETIMEDOUT: A connection attempt failed because the connected party 
did not properly respond after a period of time, or established connection failed 
because connected host has failed to respond. - connect(2) for "api.rubygems.org" 
port 443 (https://api.rubygems.org/specs.4.8.gz)

It must be proxy setting that we use to access Internet. Is it possible to make Ruby to honor these settings?

Update 2.

C:\Windows\system32>gem sources --add http://rubygems.org/
https://rubygems.org is recommended for security over http://rubygems.org/

Do you want to add this insecure source? [yn]  y
Error fetching http://rubygems.org/:
        Errno::ETIMEDOUT: A connection attempt failed because the connected part
y did not properly respond after a period of time, or established connection fai
led because connected host has failed to respond. - connect(2) for "api.rubygems
.org" port 80 (http://api.rubygems.org/specs.4.8.gz)

Answer 1

Do

gem sources --add https://rubygems.org/

and try again