With Streaming Stick model 3810, released in 2017, Roku enhanced the WiFi receiver and moved it from the interior of the stick out into a bulge in the USB power cord. For this and later Streaming Stick models, a specialized power cord with a "Long Range Wi-Fi Receiver" must be used. Without it, the stick cannot connect to the internet, nor can it communicate with its remote.
There are two different power cords with Long Range W-Fi Receiver available, depending on your Streaming Stick model. The two are NOT interchangeable.
Roku Community Streaming Expert
I am not a Roku employee, only a user like you. Please, no support questions via private message -- post them publicly to the Community where others may benefit as well.
If this post solves your problem please help others find this answer by clicking "Accept as Solution.".
Ultra 4800 | Streaming Stick 4K+ 3821 | TCL Roku TV 43S245/C107X
