we have finally upgraded our mac to 10.6.8, it got issue for a long time…… since we have installed virtual box, however during the upgrade, it reported that virtual box crashed the upgrade.

we removed the virtual box but the issue still unresolved.

hence, what we do is to upgrade the virtual box to the latest version, and the upgrade is succeed.

But, the upgrade still have issue, after the machine reboot, no icon and no login dialog is prompted…… finally, we search on the web and we find out the solution: http://support.apple.com/kb/TS1411

we have to go to safe mode (hold the shift key), then do the follow thing after open the terminal: (for Mac OS X 10.2.8 or earlier) mv /var/db/SystemConfiguration/preferences.xml preferences.old

(for Mac OS X 10.3 through 10.3.9) mv /Library/Preferences/SystemConfiguration/preferences.plist preferences.old

we don’t know why we have to do that……for normal user, they may go to pay several dollars to the support for the fix..