Can't ssh

["John Fleming" <john@wa9als.com>]

Since yesterday I can't ssh in to my Debian unstable box, fully upgraded.
When using Putty, as soon as the terminal window opens, it immediately
closes.  This is true whether from another machine on the LAN, or from a
more remote machine.  I've checked with and without my Firestarter
firewall - no difference.  SSH is running.

Interestingly, the Linux box is also not serving my webmin page on port
10000, but it IS serving my virtual hosts on port 80, and POP and IMAP mail
on their respective ports.

I don't see what's common to all of this.  Where else to look for problems?
Other than upgrading unstable, I haven't installed anything new or otherwise
changed a previously working configuration.  Thanks - John AKA talk newbie
to me...