It can happen. Your Siri Remote isn't working. You're sure it has a good battery charge. As (bad) luck would have it, it may have become unpaired with the 4G Apple TV. Here's how to get the two paired up again.
Image credit: Apple
The applicable Apple Tech Note is HT204185 Here's a summary.
1. Place the Siri Remote within 3 inches (about 75 mm) from the Apple TV and point it at the Apple TV.
2. Hold down the MENU and VOLUME UP buttons for 5 seconds. Note that these buttons are placed diagonally from each other, so you might need two hands.
3. Quickly look at the top righthand side of your TV screen. If all went well, you'll see a message: "Remote Connected." The message disappears after a few seconds.
If that doesn't work, if available, you can try using a previous generation aluminum remote, with its IR capability, until you are able to troubleshoot with Apple's tech note and further diagnose the problem.