In a computer any devices (example: DVD Writer, Display, Network card or Ethernet card or any external devices attached, etc) to work properly you need to install driver for that particular device. If you are facing problem with any devices not working properly or not getting detected properly, then you might have not installed the device driver properly or if already installed then the device driver might have been corrupted or the device hardware itself should be having a problem. All the computer hardware components or devices installed successfully or unsuccessfully can be viewed in DEVICE MANAGER.
To open DEVICE MANAGER, go to "START" and click on "SETTINGS" and click on "CONTROL PANEL" to open CONTROL PANEL window. Inside CONTROL PANEL window double click on "SYSTEM" to open "SYSTEM PROPERTIES" window. In the "SYSTEM PROPERTIES" window click on "HARDWARE" tab. Now you should be able to see a "DEVICE MANAGER" button.
In the device list if any device which has a yellow question mark with exclamatory symbol on the left side of the device name as shown below, means that particular device is not installed. In order to make that particular device work properly, you should install driver for that device. In the below image you can see that there is a yellow question mark with exclamatory symbol next to "EHTERNET CONTROLLER". This means the network or ethernet driver is not installed. In order to make the ETHERNET CONTROL work, you need to install the ethernet or network driver.