Why does my computer crash when I use 2 memory sticks? [duplicate]

Possible Duplicate:
Installing two RAM sticks causes problems; using only one of them doesn't?

Motherboard: P7N SLI Platinum Memory sticks: 2x DDR2 PC2 6400

It works fine with one stick in, but if I but both in I get a BSOD after a random amount of time.

Your motherboard I would say is defective. Try and run Memtest86 with both sticks in and see if you get any errors, then run it with just a single stick. If you have access to another stick of RAM (maybe a friend?), try running it with the first and the loaner stick. It may be that your second stick of ram is defective and not your motherboard.