1.) Type dxdiag in Windows search bar, press enter, and click 'Save all information' after the utility runs. Open the saved file and make sure it says 'Miracast: Available, with HDCP' in the System Information section. If it says Miracast is not available, screen mirroring won't work.
2.) Type network reset in the Windows search bar to reset your PC's network settings. Reset the Roku device's network settings at: Settings > System > Advanced system settings > Network connection reset. Re-enter network credentials as required.
3.) If screen mirroring still doesn't work after resetting network settings, you could try powering down (unplug if possible) both your PC and Roku device, and then power them back up.
4.) A last resort option would be doing a factory reset of the Roku device. There's also a Fresh Start option in Windows 10, but if you can see other Miracast devices, it doesn't seem like Windows should be the problem.
Mirroring Windows to a Roku device has always been hit or miss, mostly miss. It uses the Miracast protocol, and not all computers have the correct hardware to support it. You'd be far better off just running an HDMI cable from the laptop to the TV than messing with screen mirroring. Not as convenient, I agree. But it will work every time that way.
I've honestly only had a problem like described in these posts just one time, on a Roku3 at my father's house and I didn't spend much time trying to sort the issue. Every other time I've been able to cast to Roku devices in my home nearly without fail for years, 4 different laptops, 2 android devices casting to (over time and versions) 3 different TCL Roku tvs, a Roku Ultra, a Premeire, an original Streaming Stick, and (ironically) the very same Roku 3 unit that was problematic on my father's network. (I'd love to say I investigated the variables at play between the successful connects with that one at my house versus my father's house, but never go around to.) Ultimately I agree though. Just picking up a nice long HDMI cable is the path of least resistance by a mile. I have one stored in my TV console just for that reason (in case).
Re: Can't screen mirror from Windows 10 laptop to Roku
Finally got Windows 10 to find my Roku and connect. The typical instructions were missing a couple of steps. Here's what worked for me:
(1) Set Roku screen mirroring to "prompt first" (NOT always); (2) RE-BOOT ROKU; (3) Go to PC action center and click connect; (4) NOW your PC will list your Roku device, but it still won't connect until you; (5) Go back to Roku settings and change to "Always."
Please help Re: Can't screen mirror from Windows 10 laptop to Roku
Please help. I did everything in the OP.
My 50" Onn Roku TV WILL connect to my laptop and ask permission to mirror, but when I say yes it starts connecting and then stops and goes back to the settings screen. Then when I look back on my computer to see the list of devices to connect to, it's still there as an option and just stops. :/