Some networks have channel modes (subset to the network services) that only allow registered users to speak in the channel, let alone join, but my bet maybe the channels are muted by default or some funky channel/user mode prevents people from sending text for some reason. If there aren't issues with other networks, I'd have to conclude to that being the only possible problem after Russ's suggestions didn't help.
New provider, new host. Not identified with nickserv? Not registered to speak in certain channels with that host? I've seen it before.. all these new funky irc modes developers are inventing.
