I can't believe it, I've found the answer!
I read this page (
http://bytes.com/topic/networking/answe ... -cant-ping) and it prompted a thought. Some time ago, I had installed a VPN client on my home PC in order to tunnel to work when I was not at the office. After I had finished using it, I disabled it, so it wasn't in use or running (I thought). However, I have now discovered that by uninstalling the software completely SS is accessible within and without my network

I believe that perhaps the VPN had a firewall of sorts that was active even when the client was not running.
Of course my work laptop also has the VPN client installed, which is why neither machine responded to pings.
What a hassle! Hope my discovery is useful to others, and thanks to those who helped me narrow down the problem.
p.s. minor issue now: whilst writing this, I have been listening to my music collection thro my phone and it seems that the tracks can randomly jump and/or finish early. oh well, one more bug to hunt
