High cpu usage for internet exlore

I have been looking at the form and can't find and answer to my problem. I get the pop up from Norton about the high CPU usage and my computer slows way down and sometimes freezes. I am running Norton the new version 5.1.0.29. Now what I am doing, when this happens is I am on Farmville or one of Zanya games on Facebook. And the only way to resume play is to close all browsers and put my computer to sleep, then wake it up. Sometimes I have to do this 2 or 3 times to be able to even open my homepage at a normal speed. I have windows 7 and I am running explore 7  my lap top is only 3 years old. I have

Processor Intel(R) core TM 2 Duo CPU p7350 @ 2.00GHz  2.00 GHz

Installed Memory (RAM) 4.00 GB (3.87 usable

System 64 bit

When I look ant my control panel it says for the hard disk drive 178 GB free of 286 GB and the blue bar is showing less than have way full

Norton 360 is the only security on my computer.