Symptom
Your computer does not connect to the Internet, or to your local area network (LAN). This is noticeable immediately after startup. You may also notice one or both of these symptoms:
1. IP address, subnet mask, and router address have all been set to "255.255.255.255".
2. DHCP configuration is not available as a choice in the Network preference pane.
Solution
Install Network Update 1.0. For information and software download, see technical document 106922, "
Mac OS X: About Network Update 1.0".
If the issue persists, follow these steps:
Important: You must be logged in as an Admin user.
1. Click the Finder icon in the Dock.
2. Choose Go to Folder from the Go menu.
3. Type: /Library/Preferences/
4. Click Go.
5. In the Finder window, locate the file named: com.apple.PowerManagement.plist
6. Drag this file to the Trash.
7. Restart the computer.