@Gamermom08 You are asking for a step by step instruction on how to add a hard drive, correct?
If so, you need to remove the Access Panel, Front Bezel and Drive Cage Bracket first. Then you can add the hard drive. You will probably have to places you can add the drive to. You can add it to either spot.
Note 1: it may or may not have screws in place to mount the drive. 3.5inch HDD's use standard #6-32 UNC screws if needed.
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