The most common causes of this are loss of power to the fiber terminal (ONT) or an unplugged network cable. The other end of this cable should be plugged into the active wall jack or. Fiber optic troubleshooting is an essential skill for network administrators, technicians, and engineers responsible for maintaining and repairing fiber optic systems. These high-speed, high-capacity communication networks are increasingly replacing copper cables, offering superior performance and. That blinking red LOS light means your router has lost its connection to your internet provider's network. Before you panic or call tech support, there are several simple fixes you can try at home that often solve this problem in minutes. ”. When your fiber optic network stops working, begin with a structured approach. Many fiber internet problems come from dirty connectors or loose plugs, not major faults. By following these instructions, you may be able to restore your service without the need for additional support. This guide covers what to verify before you start, followed by six fixes to help stabilize your.