Hi Sansri, try booting in save mode and set the Startup Options to "Symantec Antivirus", instead of "System". This will delay the start of SAV a bit and should help you getting the PC into the Login window.
You can find this option in the Configure > Filesystem AutoProtect > Advanced
If this helps you have a conflict in the startup processes with another program. You can use Tools like Autoruns (Sysinternals) to compare machines that do work with the ones that don't.