RAM and MOBO

[terminater]

OK so in my pc I have an Gigabyte mother board with amd fx 6300 CPU and 12GB of ripjaws RAM but in windows it only let has it saying that there are 8GB usable so I moved the RAM around and same thing. But, once I got a certain config it had 12GB usable but, it would blue screen after five minutes. I thought it was the MOBO so I returned it and got a replacement one only to find it has the same problem with it all. I am starting to think it is because I have 3 ram cards but I really don't want to buy RAM until I am sure that is what it is. Any idea's? thank you in advance.

[RainfallWithin]

Try putting only one RAM stick into your motherboard at a time and check that each one is recognised in the BIOS and in Windows.

[terminater]

OK thank you I will try that.