Yesterday it pinged out and, since then, just cycles through its server list, always displaying the message: "Timeout: connect to abc.server.xyz" where "abc.server.xyz" is one of the servers on its list.
I've restarted but to no avail.
Any clues or suggestions as to what has changed/gone wrong?
Check your my-ip settings in your .conf .. It could be your shell provider got a new subnet and thus ip's possibly changed.
It could also be that the admin has null routed the ip you are using due to DDoS attacks, in which case you should use a different vhost/ip.
If this doesn't work, you should speak to your shell admin.