Restarting your router, checking your modem connection, and resetting network settings often resolve the problem quickly. Why Do Fiber Networks Fail? Despite their robustness, fiber networks can fail due to:. This connected but no internet error means your device has successfully authenticated with your router and received an IP address, but it cannot reach anything beyond your local network. The problem affects Windows PCs, Macs, iPhones, Android phones, and every other WiFi device equally. First, check the basics—look for power issues on your optical network terminal and inspect all cables for visible damage. Many fiber internet problems come from dirty connectors or loose plugs, not major faults.