When I had this problem some time back on my old computer, I finally tracked it down to my firewall. After spending hours trying to diagnose the problem, I gave up and just uninstalled all of the Symantec software and reinstalled it. The firewall was Norton/Symantec and I'd tried tweaking it for something and had reset some value that wouldn't let it connect. Reinstalling it all meant it worked together, and reset the defaults.

SRS