Chosen Solution
Following the iFixit instructions (and with a helpful hint from Dan), I managed to replace the original WD hard drive in my EMC 2389 21.5 inch iMac. I put in a new WD 1Tb drive and added 4Gb RAM. As far as I could tell, all connectors were replaced correctly. But when I pressed the start button and held down Command / R, nothing happened. The external drive on which Time Machine is installed blinked repeatedly (three flashes then rest), but nothing else. How do I troubleshoot this?
Did you ensure that the RAM you bought was compatible and matching with the other stick of ram?
