There are a number of reasons why your external hard drive might not be recognized. The most common reason is either a malfunction of the device, or a problem with the operating system you are using.
First, check the connections between your external hard drive and your computer. Make sure that the USB cable is firmly connected and the power cord matches the correct voltage. Additionally, check whether the USB port of your computer is functioning correctly. You can test this by trying to connect other USB devices, such as a flash drive, to see if they are detected.
If all the connections are working fine, then check to make sure your external hard drive has power. Look for any indicators that the device is powered on, such as a light either on the device itself or the power adapter. If the power indicator is not on, and your power adapter is plugged in and the appropriate voltage is selected, try a different power adapter and check the connections again.
If your device appears to be powered on, check to see if it is detected by the operating system. Open up the File Explorer/Finder, and see if your external hard drive is listed in the list of drives. If it isn’t showing up, there may be a problem with the device driver. Try reinstalling the device driver, or manually specifying the device driver if necessary, to see if that resolves the issue.
If your external hard drive is still not showing up, the issue could be with the formatting of the hard drive. Check to see if it has been formatted with a file system that is compatible with your operating system. If it hasn’t, you may need to reformat the hard drive. Be sure to back up your data first before reformatting, since reformatting will erase all the data stored on the drive.
If these steps do not resolve the issue, the problem could be more serious, such as a corrupted or damaged hard drive or a malfunctioning controller board. In these cases, you should take your external hard drive to a computer professional who can diagnose the device and determine what needs to be done to repair it.