Make sure that the batteries are a fresh pair and have the same brand as each other. Using two batteries with different brands can cause one to empty before the other, leading to the remote not working.
Your remote may not be paired with your Roku device. Try re-pairing your remote by removing the battery cover and holding the pairing button until you see the pairing LED flash. If done correctly, a remote pairing notification should appear on your screen.
For additional information and troubleshooting support, check out the [[Roku 3 Troubleshooting#Section_Remote_Control_Not_Responding|Remote section of our troubleshooting guide.]]