NIS 2011 slows down laptop

my laptop is toshiba satelite, i am using NIS2011, still have 63 days to expiry date but there is warning: your NIS scan program expiry and no longer to use.

other thing, every time i used internet for fiew hours, my laptop become slow and slower and slower till it is became freeze..

i must shutdown my laptop, and start again and soon and soon..but its still running slow or even freeze again, till i make full scan and use Norton Power Eraser..it will run normal, and again appear problem in futures..

hope somebody can help my problem,,or i must used another anti virus? thanx..

 

 

[edit: Clarified subject.]