turn off problem

I have a toshiba satellite laptop with windows xp, I have installed norton antivirus. but after installing some programs, when I try to turn off the computer the system halts, and I have to turn off manually by pressing the power button until it is off.

if someone knows how to fix this problem please help me.

thanks

what is running  in the task manager when you switch off? ctrl alt del?have a look is maybe norton?