Issue with upgrading Norton 2010 to Norton Internet Security 2011

I installed Norton Internet Security 2011 when my subscription to 2010 expired. The install was uneventful. However, my system has become slow and after about 15 to 30 minutes of inactivity, my screen saver starts up and that's it: -  my PC freezes. The only solution is to turn the system off, wait a minute and turn it back on again.

 

  • DEll XPS420
  • Vista Ultimate 32 bit
  • 4 GB DDR2 
  • Other than Norton, no other antivirus software is/was installed

My research indicate that the suggested solution is to uninstall Norton 2011 and reinstall it? Can this possibly be correct? That is to say, why didn't it work the first time around?  I am eagerly awaiting any feedback that might provide a better and perhaps simpler solution rather than having to uninstall, reinstall and reconfigure Norton again.

 

Thanks in Advance!