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