Hi I have MacBook MC240LL/A Model A1181 (EMC 2330) Family Mid-2009 ID MacBook5,2 Yosemite os I upgraded my memory to 6 gb. The problem is the system graphics gets pixelated ( lack of better description) and then the machine freezes. I can still move the mouse around but not much else. Sometimes it will unfreeze for a bit. It seems to act ok with 4gb of ram The original memory was Hynix 2rx16 pc2 6400S-666-12 The new is pc2-6400s ddr2-800 256mx64 I am not familiar with all the memory terms etc so I don't know if something here would stand out to you folks as a problem. If not would you have any suggestions on how to fix this problem? Please be kind as I am not Mac literate as I am trying to fix my daughter in laws machine. So please be simple with your explanations.