An alert box with this message appears after you turn on the computer:
If you are using America Online to connect to the Internet, update to America Online 5.0 or later.
If this does not resolve the issue, see technical document 24877 "Mac OS: Modem Unexpectedly Dials", which describes TCP/IP services that may unexpectedly attempt to initiate an Internet connection. These services may need to be disabled or reconfigured as outlined in the document.
If you are not using America Online as your primary ISP, use the Extensions Manager to turn off the AOL Link Enhanced extension.