The icon in the system tray says I'm connected, but I can't seem to use any program that requires network access. In particular, firefox and ssh can't find any network resources. I've used the GUI 'about this connection' option to check for proper address assignments, and everything seems to be right and proper from the point of view of the network manager.

The trouble started after I messed around with the configuration to get it to share the connection with another computer. I haven't had to use that connection recently, so I don't know if that might be working instead, although the two shouldn't be mutually exclusive.

My questions:
1) any idea what might be causing this?
2) if not, how might I reset the internet settings back to what they used to be?