Dell Dimension E521 - Manual (Page 29)

4. Align the hard drive bracket with the guides in the hard drive bay.
5. Gently slide the drive into place until you feel a click or the drive is securely installed. Take care not to let the drive free-fall into the drive bay.
6. Connect the power and hard-drive cables to the drive (see Connecting Drive Cables ).
7. Check all cables to be certain that they are properly connected and firmly seated.
8. Replace the computer cover (see Installing the Computer Cover ).
9. Connect your computer and devices to electrical outlets, and then turn them on.
See the documentation that came with the drive for instructions on installing any software required for drive operation.
10. Check the System Setup for drive configuration changes (see Entering System Setup ).
1 drive 2 hard-drive bracket
1 hard-drive bracket 2 hard drive 3 guide in hard-drive bay
1 serial ATA data cable 2 power cable
NOTICE: To connect a network cable, first plug the cable into the network port or device and then plug it into the computer.