Ok I have figured out that my CPU only supports up to 1333MHz, which sucks.
What I still dont know is the 4gb issue.
I will check the RAM is seated properly, I will also check for bent pins on the mobo and CPU.
I also have another issue. I have a Sapphire HD 6870, and after installing the drivers I get a black screen after reboot. I have tried installing from the Sapphire site and the ATI site and I get the same problem.