Are you connected to Campus WiFi or Ethernet?
Have you tried resetting your browser to factory settings as you may have a plug-in or extension preventing the XFINITY Stream player to load?
For Chrome users, is tv.xfinity.com saved as one of your "allowed" sites to use Adobe Flash?
For directions on how to do this visit here.
If using the mobile app, have you tried to delete it from your device and re-download it from the app store?
For issues related to Roku devices, please click here.