I have a late 2007 MacBook running Leopard and recently decided to do some upgrading. I first cloned my hard drive onto a larger hard drive and installed the new hard drive with no problems. I then decided to upgrade my 2GB (2 x 1gb) ram to 4gb (2 x 2gb), supposedly my MacBook can handle up to 6GB (1 x 2GB + 1 x 4GB). The new RAM is the correct type of RAM but I am still having problems with it. At first I tried installing both sticks and it did not work. Then I tried installing just one stick and leaving one slot empty and this did not work with either stick in either slot. Then I tried installing one new stick (2gb) and one old stick (1gb) and it worked. Further I tried this in every combination of 1 new stick and 1 old stick in every slot and chip combination and they all worked. I've tried resetting the PRAM many times as well as the SMC, but I can never get both new 2GB to work together. Any Suggestions?