NIS 2011 Freezes desktop - Have to reboot

I installed Norton Internet Security 2011 yesterday and my desktop has frozen twice. The only way to un-freeze the system is to reboot. My system configuration consists of:

 

Windows XP Professional SP3

4 GB of Ram

100 GB Hard Drive

 

The previous security software was completely un-installed and the desktop was re-booted before installing NIS 2011. This problem started to occur after installing NIS 2011. What's causing this? I didn't purchase this software to encounter problems.  I need reliable software!