System slow; PF usage keeps increasing

Hello,

My system has become too slow and in task manager when I check my PF usage keeps increasing.
Also couple of days back internet windows kept poping up. I restored my system back to last week, this problem solved for a while. I installed Norton Internet security and scanned entire disk. It identified more than 10 viruses and fixed it. But when I tried to restart the machine it did not shutdown. I did hard shutdown then tried to restart the computer. It took long time to open the windows, now the system is slow.

Please help me on this.
Thanks,
-Balu