Your router might be programmed in a way which does not allow VoIP signal to go through, or it is blocked by firewall settings. Please check your router settings. Our technical support can also help you to some extent, but this does depend on the type of router you use.
This can also happen if you're not using a regular router, and are using a switch, hub, or any other device that doesn't assign local IP addresses and doesn't access multiple devices simultaneously. If that is the case, please try our phone adapter on a regular router.