Instructions
Ensure that the Xbox 360 hard drive is firmly attached to the top of your console. It should rest with all of its edges flush with the console.
Check to see if the Xbox is recognizing the hard drive by cycling the power off and on, and then navigating to the Memory menu on the Xbox 360 dashboard by selecting “My Xbox,” “System Settings” and finally “Memory.” Your HDD unit should be listed.
Turn off the Xbox 360 console and press the small button on the front of the hard drive to release the drive from the system. Pull the drive upward to remove it.
Turn on the Xbox and wait until it reaches the Xbox Dashboard. Next, power the system down again. Attach the hard drive to the system again, turn the console on and proceed to the Memory menu to see if the HDD is listed. If nothing shows up, you may need to try another console or hard drive for further troubleshooting.