Hi,
 
I've just built myself a new system:
 
Intel E8400 (retail heatsink)
Asus P5N-D
NVIDIA 8800 GT  
8GB OCZ PC6400
Vista Ultimate 64
 
When I run the Windows Experience Index I get the following result:
 
Processor: 5.0
Memory (RAM): 5.9
Graphics: 5.9
Gaming graphics: 5.9
Primary hard disk: 5.7
 
According to Tom's Hardware CPU Charts (http://www23.tomshardware.com/cpu_ [...] &chart=442) I should get a Processor score of 5.7. I've also confirmed this with a friend who has an E8400 too.
 
Any ideas why my CPU score is so low?
 
Any help would be very appreciated.

Maybe it didnt clock up when it was tested?

Don't go by the WEI, it's worthless. If you really do need to see figures, try running some CPU benchmarking software, like SuperPi, or maybe try 3dmark06

Go into BIOS, disable SpeedStep and C1E(might be wrong). Then try again. Cuz my Q6600 at 2.4GHz stock gets a 5.9.

Even if I agree with Kraynor about WEI being worthless, I can still be a symptom of something being wrong. I wouldn't have worried about a 5.6 or even a 5.5, but scoring 5.0 when you should have got a 5.7 could mean something.
 
First make sure your CPU runs at the right speed (333MHz FSB + x9 multiplier = ~3GHz or, if idle, 333MHz FSB + x6 multiplier = ~2GHz). I know some older MB used to sometime default to lower FSB if some events occured, for example, if yours was to default to FSB 266 (1066), your CPU yould run at 2.4GHz top.
 
Also check that there were no CPU hungry application running in the background like a Virus scanner running a first full system scan for the first time or a Windows Update installing stuff. Just basic IM or live scanner shouldn't matter.

---------------
The capacity to learn is a gift; The ability to learn is a skill; The willingness to learn is a choice.  - Rebec of Ginaz

So I found a solution in the end.
 
I checked the bios multiplier / fsb speed and ever seemed ok.
 
I then upgraded the bios to the latest 0402 version (came out on 21/03/2008) and after doing this I noticed the multiplier was set to x6. Changing this back to x9 seems to have fixed the problem and I'm now getting 5.7 in the WEI.
 
Thanks for the help