Hey Olive, let's work through this systematically to pinpoint why your Ethernet connection died suddenly—no need to guess, we can test each part step by step:

第一步：快速排除线缆本身的问题 #

• Grab a known-good Ethernet cable (one you've confirmed works elsewhere) and plug it between your computer and the wall RJ45 port. If your network comes back online, the issue is definitely with your original cable—either the RJ45 connector was crimped poorly (like wires not fully seated under the pins) or the twisted pair has internal damage.
• Inspect your original cable's RJ45 ends closely: look for loose wire strands poking out, bent metal pins, or any signs the connector was pulled/knocked hard. If the pins are deformed or wires are loose, a new crimped connector will fix it (just make sure to follow T568A/B wiring standards when re-crimping).

第二步：排查墙内端口与设备兼容性 #

• Try connecting a different device (laptop, another desktop) to the same wall port. If that device also can't get network, the problem is likely in the wall's internal wiring or the RJ45 module behind the panel:
  • Carefully remove the wall plate (unplug any nearby power sources first for safety) and check the module's wire connections. Look for loose wires, oxidized metal contacts, or wires that were crimped into the wrong slots. Oxidized contacts can be cleaned gently with a cotton swab and isopropyl alcohol, but if wires are misaligned, you'll need to re-terminate the module.
• If other devices work on this wall port, double-check your original computer's Ethernet status:
  • On Windows, run ipconfig /all in Command Prompt—look for your Ethernet adapter to see if it says "Media disconnected" or fails to get an IP address.
  • On Linux/macOS, run ifconfig -a or ip link show to check if the adapter is listed as "down" or has no assigned IP. Sometimes a hidden driver glitch can cause this, even if you thought you checked earlier—try disabling and re-enabling the Ethernet adapter in your system settings.

第三步：检查上层网络设备 #

• Locate your router/ONT (optical network terminal) that the wall port connects to. Check the Ethernet port light:
  • If the light isn't on at all, there's no physical connection—either the internal wall wiring is broken, or the router/ONT port is faulty.
  • If the light is flashing erratically (instead of the steady/regular blink of active traffic), try restarting the router/ONT. Unplug it for 30 seconds, plug it back in, and wait 5 minutes for it to fully reboot.
• If you're on a shared network (apartment complex, office), ask nearby users if they're also having outages. If everyone is down, the issue is with the building's main switch or your ISP—submit a support ticket right away.

第四步：测试线缆通断（如果有工具） #

• If you have a cable tester (the small handheld device that tests each twisted pair), plug both ends of your original cable into the tester. It will show if all 8 wires are conducting properly:
  • If one or more wires show as "open," that means there's a break in the cable or a bad crimp.
  • If you see "crosstalk" warnings, the twisted pair's insulation might be damaged, causing interference that disrupts the signal.

备注：内容来源于stack exchange，提问作者Olive