I am also having this issue. Sony Vaio VGN-CR42Z just shuts down without warning. I have noticed a lot of disk activity just before it shuts down. It is not overheating as the laptop has only just booted up in some instances. My laptop is almost 3 years old and this problem did not start until last November (2.5 years old) and has got steadily worse. I have done diagnostics and also a full system restore but to no avail. Sony have now asked me to send the laptop into them but will charge me £60 just to disagnose the issue. Surely if the issue is with the laptop itself and other people are experiencing the same problem this should be recognised by Sony? Please help!