migsb

Hi,
I have been having system crashes when I use both sticks of Corsair ddr 2 /667. When I use either stick separately they work fine,but when they are both slotted into my pc then a crash will eventually occur. I have tested them and each stick is fine. Only when they are both used together do I have the problems. My mother board.....Asrock 4 dual core Vsta is able to support 2gb or ram but does not like them working together for some strange reason. Can anybody give me any advice on what the problem may be? Thanks.