Hard drive continuosly running

Hello All,
I'm new to this forum and was hoping for some help. My computer has slowed down almost to a crawl. It takes about 30 seconds for my internet explorer to open then at a snails pace. I can hear my hard drive running continuosly, but the task manager shows that nothing is running. I have a cable modem and have run every spyware remover imaginable along with both norton and mcafee antivirus'. My cpu usage at times shows 100% when nothing is open. How can I find out what has taken control of my cpu and get rid of it.
Thank you in advance for any suggestions.
Pete

Might as well run a HijackThis log by the Pros over in that section.

Instructions here:

http://www.techhelpforum.com/showthread.php?t=3702


If they give an all clear we can pursue other options such as a hard drive diagnostic etc.

Thanks!!
Pete