In some cases, after applying a security update or other major installation, Mac OS X can unexpectedly begin searching for a non-existent network server at startup. MacFixIt reader Lynne LaMaster writes
"One of my clients used Software Update to do the latest security update. When she went to restart her computer, she said it made an awful noise (she has a dual 1.8 G5) and she was afraid something really bad was about to happen.
"She restarted it again, but got a blinking world icon, and couldn't get to her hard drive. As a new Mac user, she was pretty panicked.
"Here's what we did: Restarted holding down the option key, which found the correct system. We selected that, and it started up correctly. Then, in System Preferences, we clicked on the Startup disk, and found that it was searching for the network server (which doesn't exist). We reselected the correct system, and all was fine."
On a related note, if you are noticing that your Mac OS X system is starting up more slowly than usual, and seems to stall for a long time on the network initialization phase, you may need to disable some unused ports.
Open System Preferences, and go to the Network pane. Then use the pull-down menu next to the word "Show:" to select Network Port Configurations. Disable any ports that are not in use.
If you have two or more connection types regularly (for instance, if you use an AirPort connection but sometimes link directly to Ethernet), place the most often used configuration above the less used configuration so that Mac OS X will recognize and utilize it without waiting. The configurations can be dragged and dropped.