Same problem. Turns out the router just needed to be restarted. Problem solved.
TV says NO SIGNAL. Light on Roku device is off. I turned off TV and Roku device. After turning back on, light flashed but wouldn't stay on. Then I swapped out the Roku device from bedroom to the living room - same problem. Then I went to Target and bought another Roku device. Same problem. And to make matters worse, the bedroom Roku also wouldn't work. Then I powered off both TVs and powered off the router, waited 30 seconds, then powered the router back on. Once I saw internet connectivity on my PC, I powered the TV and Roku device back on. Everything is working again. 🙂