"Could not find a valid gem in any repository" (rubygame and others)

I've been trying to install this 'rubygame' gem for some time, but whenever I use the command

gem install rubygame

it will give an error:

ERROR:  Could not find a valid gem 'rubygame' (>= 0) in any repository
ERROR:  While executing gem ... (Gem::RemoteFetcher::FetchError)
Errno::ETIMEDOUT: Connection timed out - connect(2) (http://rubygems.org/latest_specs.4.8.gz)

I've also tried other gems but with similar results:

ERROR:  Could not find a valid gem 'rake' (>= 0) in any repository
ERROR:  While executing gem ... (Gem::RemoteFetcher::FetchError)
Errno::ETIMEDOUT: Connection timed out - connect(2) (http://rubygems.org/latest_specs.4.8.gz)

I've already made sure I have an internet connection, and have already tried reinstalling both ruby and rubygems (currently using ruby 1.8, rubygems 1.7.2). Googling didn't help me at all. I would be very grateful if anyone can solve my problem. My sources list only shows http://rubygems.org