To open your CPU case and install a new hard drive, follow these steps: 1. Shut down your computer and unplug it from the power source. 2. Locate the screws holding your CPU case together and remove them. 3. Gently slide off the side panel of the case to reveal the internal components. 4. Identify an available bay or slot where you can install the new hard drive. 5. Connect the hard drive to your motherboard using a SATA data cable. 6. Connect the hard drive to your power supply using a SATA power cable. 7. Secure the hard drive in place using screws or other attachments provided. 8. Replace the side panel of your CPU case and secure it with the screws. 9. Plug in your computer and turn it on.