Well I'm pretty sure that the Gnutella network isn't down, since it's decentralized

If you actually are saying that you didn't even try to restart your PC and modem, then that would most definitely be a good idea to try now.

It could be that your ISP has started blocking Gnutella. Maybe try some other Gnutella clients, like e.g. Phex or the old BearShare (links in BearShare section)