There are a few possible reasons for this. 

  • Make sure you're using a Canon: PBU only supports Canon DSLR cameras. Other cameras will not function with the software.
  • Be sure to REFRESH: In the Camera tab in PBU, under DSLR, click the Refresh button. If you started PBU before powering on your camera, PBU might not have noticed. 
  • Restart your PC (and PBU): Try turning it off and on again. Sometimes that just does the trick.
  • Make sure the Camera is set to Manual Mode: Be sure that your Canon camera is set to Manual and not to Video or another setting. It has to be in Manual in order for PBU to interface properly.