When starting up the computer from a powered-off state (such as directly after installing RAM) the computer will fail to produce a startup chime and hang during the start up process. At that point, perform a warm restart by pressing the reset button on the front of the computer and it will reboot successfully.
Note: The startup chime will still not be audible.
Apple is investigating the issue in order to provide a permanent resolution. In the interim, this issue can be avoided by putting the computer to sleep instead of shutting it down.