Possibly your remote has died, but it may have just lost its pairing to your Stick and needs to be re-paired.
You may find your Roku is only receptive to the pairing request from the remote for a short period of time after it starts up. Try pulling the power to the Roku for a few seconds then plugging it back in and waiting for it to start up before reinserting the batteries in the remote and pressing the pairing button.
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.".
Streaming Stick 4K+ 3821 | Streaming Stick+ 3810 | TCL Roku TV 43S245/C107X