http://www.centon.com/memory/products-ddr2/4GB667KITLT I'm trying to upgrade my Mac's RAM and I'm running into a problem. When I install both 2gb sticks of RAM into the machine, it will not start up. If I install only one 2gb (I've tried both) and leave my original 1gb in place, it will start up with no problem and the system recognizes the fact it now has 3gb installed. How do I fix this? Is it because my RAM isn't compatible?