Here are a few steps you can follow to try and resolve the error:

1. Restart your router: disconnect from power, wait 10-15 seconds, and then power on the device again.
2. Check your cables. Ensure that all necessary cables are securely connected.
3. Check your IP address. Sometimes, an incorrect IP address can result in a DNS server not responding error message. To make sure you have the correct address, contact your ISP.
4. Check DNS Settings. Make sure that the DNS settings of your router are correct and match those provided by your ISP.
5. Flush the DNS cache on your computer. This can help resolve any DNS issues you may be experiencing.