With a Streaming Stick, you need to use a Roku Voice (rf/wifi) Remote in order to communicate with the Roku device.
The Long-Range Wireless Receiver (LRWR) that is built into the power supply cable for the Streaming Stick provides for both the connection to your network/router (wifi) and for providing a hidden, private network for the Voice Remote to connect to.
So, your culprit could be either a bad Voice remote, a bad LRWR, or a loss of communication with your network/router.
Try unplugging the LRWR from the device and reseating the connections. (if the power cable is plugged into the USB port of your TV, try using a power adapter at the wall outlet, like a cell phone charging adapter). Then restart your router as well.
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To replace the proprietary LRWR is about $20 and is available from Roku. To replace the Voice Remote is also about $20 -$30 depending on model. https://www.roku.com/products/accessories
Since it sounds like your device is past the one-year warranty, need to decide if the seperate purchase of components to diagnose is worth it or to replace with a new Streaming Stick 4k that is currently on sale for $35. https://www.roku.com/products/players
As I usually mention to Stick users, I generally steer clear of the Stick models due to this proprietary LRWR cable. If you use a set top streaming player like the Roku Express 4k/4k+, the wifi module is located internally so does not require/come equipped with a seperate LRWR cable. (just mentioning as an option if you want to avoid similar situation in future).
