Opening the Case Turn off the computer. Unplug the power cord. Open the case. A guide to doing so is HERE . Unplug the drive power cables from the forward edge of the power supply.
Further instructions are HERE .
Don't freak out over the info for installing memory, just look at dropping the power supply for now. If this system just came off lease or from regular use, it may have a helluva collection of dust bunnies in it. If you heard anything rolling around in the case when you moved it, find that loose object while you have the case open. People may have dropped screws in the case. To totally remove the power supply, unscrew the single screw that holds the grounding strap bracket on at the front edge of the power supply.