CPU usage issue

[YonM]

E8400
Asus P5Q (1306 BIOS)
G. Skill 2x2GB DDR2 800MHz
Western Digital 640GB (WD6400AAKS)
HD4870
Running XP-32bit

I recently built the above system and I'm having an issue whilst scrolling webpages. If I scroll through any webpage my CPU usage holds at around 50% and it feels very laggy. Another example of this problem occuring is when moving the cutomisable boxes on the BBC homepage. This happens on whatever browser (Opera/IE/Firefox) I use. I find it happening when move windows (eg. Steam windows) across the screen.

I also noticed when moving any of the volume sliders on the Realtec onboard sound software (Realtek HD Audio Manager), my CPU usages goes up to 15-20%.

I found a way to enable AHCI but the issue was still present. I tried a fresh install of XP and I'm still getting the same issue.



Any ideas as to what it could be?

 

[Dangman]

Did you install the video card drivers?

 

[YonM]

Yep, I've installed the video card drivers and have all the latest drivers

 

[Nenu]

What process is using all the CPU when this happens?

 

[YonM]

The browser itself.

EDIT: I took a test with 3dmark06 http://service.futuremark.com/...474CE586BB4FFC105994E4
SM 2.0 Score 5881
SM 3.0 Score 6954
CPU Score 2794
I also ran memtest overnight and got no errors.

 

[Nenu]

It may be the Java or Flash version you have installed.
Try updating them.

 

[YonM]

I'm using the latest version of both. :S

 

[engiNURD]

Do a repair installation.

 

[YonM]

Tried the repair installation, with no luck.

I also tried another fresh install of XP but this time pressed F6 to enable AHCI from the onset.
When it got to setting up the files it said iaAHCI.inf is missing, I retried the search for the file with no success.
So I installed back on IDE mode and checked the floppy disk and the file is on there. :S
I made the floppy using the files off the ASUS website.