To diagnose why your laptop is not recognizing your external hard-drive, it is best to follow these steps:

1. Check to make sure that the external hard drive is properly connected to the laptop.
2. Ensure that the external hard drive is powered on.
3. If the external hard drive is making any strange noises, stop use and seek technical support.
4. If the external hard drive is still not registering on your laptop, consider troubleshooting the hard drive using the computer’s own troubleshooting tool.