The playback on my laptop suddenly stopped working and screen was stuck on "video loading" when I selected a show to watch. I did call the xifinity "experts" and of course it was a big waste of time. I had rebooted computer many times and no help after receiving a "booster signal" from technician.
I did find a solution. First check out youtube on how to clear cache http://www.youtube.com/watch?v=GBsrNS2DSlc
Then go to "System Preferences" and open "Flash Player", go to "Advanced" and check "Allow Adobe to install updates". After necessary download is completed, reboot and restart xfinity. That worked for me and hope it helps others.