symptoms
Once the upgrade to OS X Yosemite is complete, the system will begin to reboot.
reason
It seems that if you upgrade from “OS X Mavericks” with “Mcafee Internet Security for Mac” installed to “OS X Yosemite”, the OS may not start (confirmed on October 16, 2014).
Workaround
After uninstalling, reboot your system. If the cause of not booting is her Mcafee, I think the OS will boot properly.
