If you are using Windows 7, you will have encountered this problem at least once. You have an ethernet cable plugged in, but the ethernet cable is not detected. This can be really frustrating but luckily there are some steps you can take to resolve the issue. The following are some ways to fix this problem so you can get back to work or play!
Check the connection
Unless you’ve been really rough on the cable, this is probably the easiest and least expensive solution. Unplug and replug the cable, and see if it works.

Check your cables
Sometimes your ethernet cable is not detected because it is not plugged in all the way. Sometimes there are little tabs that need to be pressed down in order to fully insert the cable. Make sure you’re doing this and check to see if anything else is loose.
Update your drivers
First, make sure you have the latest drivers for your ethernet card. You may need to download them from your computer’s manufacturer’s website. If you are using an ethernet card that came with your computer, then the drivers are already installed.
Check Windows Update for updates
The first thing you will need to do is check Windows updates. Windows 7 may not be detecting the ethernet cable because there is a firmware or driver update that needs to be installed. To see if any updates are available, open the start menu and go to the control panel, then click on windows update. If there are any updates you can install, download and install them.
If this does not work, continue with the steps provided below.
Reboot if needed
If you unplug your ethernet cable and plug it back in, the problem might resolve itself. If not, your computer needs to be rebooted.
Reinstall the ethernet driver
Most of the time this issue is caused by an ethernet driver that isn’t installed correctly. You can fix this by reinstalling the driver. To do this, go to the device manager and select Network Adapters. Find your ethernet adapter and uninstall it. Once uninstalled, reinstall it and restart your computer.
Install a new ethernet card
The first step you should take is to install a new ethernet card. This will be the quickest and easiest solution as long as your computer has a free slot for the card. If your computer doesn’t have a slot, you’ll need to upgrade it or buy a new one with a compatible slot.
Conclusion
You know your PC is running fine but the Ethernet cable is not detected. What should you do?
First of all, make sure the connection is right. If that doesn’t work, check the cables. Update your drivers if needed. Reboot if needed. Reinstall the ethernet driver. Finally, install a new ethernet card. Hopefully this will help you diagnose the issue with your Ethernet cable not being detected in Windows 7!