Only 3328 memory available

[ben16]

I have 4GB of RAM installed on Vista (64 bit) and only 3328 is showing in both the bios and on Windows. The change happened at around the same time as I lowered the CPU voltage but I'm not sure that this is the problem because I have raised the CPU voltage back the original level and it's still saying 3328.

Any ideas guys?

EDIT: Just to make it even more confusing 4GB is showing up on CPU-Z....

 

[ben16]

I'm using a 1900XTX. I havn't changed anything with the graphics so I don't think that's caused it.

 

[ben16]

It's on a Asus P5K deluxe mobo by the way so 4GB is supported on it.

Any ideas anyone?