Installing Symantec Endpoint Protection version 12.3.1

I have 4 Desktops Computers running on Windows XP Pro 32-bit. I am having a trouble with the Symantec Endpoint Protection when I install version 12.3.1 it is always request for a reboot. When I reboot the PC’s the log on screen from windows does not appears. What do you think is the problem? I don’t encounter this problem on older version 11.0700.
