My freezing problem is NOW solved. You can read the gory details here... https://www.nikoncafe.com/vforums/showthread.php?t=121211 Initially thought it was the memory which was eventually removed, returned and replaced. The problem turned out to be a faulty graphics card. I replaced it with the stock NVidia Geforce 6600 and all is well. Interestingly I downloaded a Widget which shows temps of various parts of the computer. Prior to switching cards the backside temp was 10 degrees higher than it is now. I thought it would be good to post this in case anyone experiences similar issues.