Well there are a couple of possibilities that spring to mind.
One is bent pin/pins on the CPU socket.
The other is a bad memory module.
The memory is easier to check so I would advise starting with that.
Memtest86+
http://www.memtest.org/Insert one stick of memory in slot 1 and run Memtest on it for at least 10 loops and if there are no errors then swap it over with the next one and continue untill you have checked all four modules.
If you have any errors the module is faulty.
If you have any faulty modules you will have to return the whole kit as they are matched.
Post back when you have done that with the results.