The most common causes of this are loss of power to the fiber terminal (ONT) or an unplugged network cable. Here's an example of LEDs to look for if you have fiber internet and an ONT: The Power LED. Fiber optic networks are celebrated for their speed and reliability, but even the best systems can encounter problems. To see how much bandwidth your ISP delivers to your home, connect a computer directly to your modem with an Ethernet cable and run a speed test. If the status light ring is off (no color), it means your router is not connected to the network. The. If you are only getting exactly 10mbps, or exactly 100mbps down via ethernet on gigabit fiber, checking the configuration on your computers network adapter is a good start. Checking network adapter configuration 1.