On 3000D hard drive.
It should be attached to a plate, which is supposed to be held in place by on screw on the inside corner.
Further then, the tray has flanges that slid in place and yes, there is the data and power cables which restrict movement.
The easy way to remove. Remove the screw. Slide the tray forward a little, pull the cables and let them just hang. Pull the tray forward the rest of the way and you should be holding a hard drive with tray attached. Turn it over, remove the four screws and reverse the process to install a new drive.
BTW, the 3000D also has a battery, under the zorro boards...pull it out!!