Serious lagging/freezing, CPU spikes

[Skepparn]

XP SP2
Core 2duo 3.0Ghz
9600GT
Asus P5K
2GB Ram
Soundblaster Extreme Audio Bulk
1x 500GB
1x 750GB
1x 80GB

I've had four XP-installations on this computer, only thing changed is I've added the 750GB.

First one I had this problem. Second one, I hadn't. But other problems developed so I reinstalled XP. And that's the third, thats when it came back. Now, I tried installing it AGAIN, the fourth, and the problem remains. The problem goes:

It's most noticable when running video or audio files. If I do, and at the same time browse folders, move files, delete files, open files, create files, install programs, the audio and video starts to stutter, the word "Stairs" pronounced by some person in a movie, comes out "Ss-t-t-t-aaaa-i-rr-r-r-rr-s-s-". I notice large CPU-spikes whenever this happens.

This is a problem from the beginning of the XP-installation, not a developing problem.
All disks have been defragmented.
It's NOT a virus.
Temperatures are normal.
Pagefile is 2GB - 4GB, and is not spiking.

Really need some help on this, thank you.

 

[Bobbye]

It's NOT a virus.

Okay- how about spyware?

Unaccountable spikes in activity would seem to indicate "something" is going on. IF the repeated reinstalls don't help, then consider a hardware problem.

Make it easier on yourself and do this:
Note the time con the computer clock when you're having the spikes: then>

Start> Run> type in eventvwr

Do this on each the System and the Applications logs:
[1]. Click to open the log>
[2]. Look for the Error>
[3] .Right click on the Error> Properties>
[4]. Click on Copy button, top right, below the down arrow >
[5]. Paste here (Ctrl V)

• 
  Errors are time coded.
  
  The Information Events are normal. They log on what's taking place on the system. The Warnings usually indicate either a temporary problem or a repeating one. The Errors are exactly that> something is happening that should not be in normal activity.
  
  Take a look and see what you have.

 

[Skepparn]

The only error I can find is when I closed down Explorer using task manager. I induced a lag, and nothing showed up.

 

[Bobbye]

Okay, but look at the corresponding Information Events. Although it may not be anything that is causing an error, you are trying to learn what is happening at those spike times. See what the 'Information' tells you.

Usually when troubleshooting any error or error message or problem, we ignore the warnings and Information Events. But we are specifically looking for Information here.