Garbled sound with my new Roku when disconnecting cable TV box

I just got a Roku wanting to get rid of my Xfinity TV service.   When disconnecting the cable TV box I lost my picture and got a list of instructions.   So plugged back in and turned off the Roku and TV while disconnecting.   Ok that worked.   Then I unplugged the cable coming from the splitter with Roku & TV turned off.   When I turned it back on the audio was garbled.   So I hooked the cable back up to the TV box which got rid of the garbled audio.   There is no power to the TV box....   I don't know what to try next.