1. Mac OS X reviews fonts in the Mac OS 9 System Folder during startup. A damaged Mac OS 9 font file may contribute to this issue. Note: Update to Mac OS X 10.2.4 or later to reduce potenial issues from damaged Mac OS 9 font files.

Start up from your Mac OS 9 System Folder or a Mac OS 9 CD-ROM disc. Drag the Fonts folder in the Mac OS 9 System Folder (not the Mac OS X System folder) out of the System Folder into the root level of the hard disk, or to the desktop. Restart the computer from your Mac OS X volume.

2. Remove third-party startup items.
a. Start up from your Mac OS 9 volume or a Mac OS 9 CD-ROM disc.
b. Navigate to your Mac OS X volume.
c. Temporarily remove third-party items from the /Library/StartupItems and /System/Library/StartupItems folders. You may wish to temporarily store items in your Mac OS X Users folder. If you are unsure whether an item is a third-party item or an Apple-installed item, do not remove it.
d. Restart from your Mac OS X volume.

3. For Mac OS X 10.2 or later, start up in Safe Mode (see technical document 107393 if you do not know how). Open System Preferences, then the Login Items pane. Select any login items shown and click Remove. Restart. If this resolves the issue, add login items back one at a time to isolate the issue.

4. In some instances, setting auto-dial may interfere with the login process. This option is set in the Networking control Panel under PPP Options by checking the "Connect automatically when starting TCP/IP applications" box. This setting can be removed from single user mode by removing the preferences file that holds the setting. Note: This is an advanced step. This will reset all network settings to default. You will need to reconfigure the Network pane of System Preferences to reconnect to the internet or your network.

a. Start up in Single-User Mode (press and hold the Command-S key combination during startup until white text appears).
b. Type: mount -uw /
c. Press Return.
d. Type:

mv /var/db/SystemConfiguration/preferences.xml preferences.old

e. Press Return.
f. Type: reboot
g. Press Return.

5. If the issue persists, follow these steps. Note: This is an advanced step:

a. Start up in Single-User Mode (press and hold the Command-S key combination during startup until white text appears).
b. Type: mount -uw /
c. Press Return.
d. Type:

mv /Library/Preferences/com.apple.loginwindow.plist preferences2.old

e. Press Return
f. Type:

mv /Library/Preferences/com.apple.windowserver.plist preferences3.old

g. Press Return.
h. Type: reboot
i. Press Return.

6. Reset certain privileges. Note: This is an advanced step:

a. Start up in Single-User Mode (press and hold the Command-S key combination during startup until white text appears).
b. When the command line appears, type: fsck -y
c. Press Return.
d. Type: mount -uw /  
e. Press Return.
f. Type: chmod 1775 /  
g. Press Return.
h. Type: reboot
i. Press Return.