I just bought a brand new roku TCL TV. I set it up on the same home wifi network as my laptop (lenovo). I am trying to mirror cast from the laptop, running windows 8.1, onto the tv. I enabled mirror casting on the tv but the TV does not show up on the list devices when my laptop performs the scan for devices. Note, other devices, like wireless printer do appear.
Some laptops will not support miracast screen mirroring even though your windows version does. The wifi hardware has to be able to make a wifi direct connection while maintaining your regular network connection and only the newer chipsets can do it.
If your goal is to view content (video/music/photos) from the computer on the TV, you can do that by enabling the windows DLNA server and using the roku media player, or installing plex or emby on both.