I have a late 2007 15-inch MacBook Pro (A1226). It has a 2.20 GHz Core 2 Duo, 5 GB of memory (a stock 1 GB stick and a 3rd party 4 GB stick), and a stock 200 GB 7200 RPM Hitachi hard drive. I have had issues with it shutting down in certain situations. (1) The laptop shuts down abruptly whenever I pick it up and walk around with it. This consistently happens within 5 seconds of picking it up. I know for a fact that this never used to be problem. I only started noticing this happening about 5 months ago. (2) The laptop randomly shuts down abruptly when I'm using it on a hard stable surface that does not block any vents. This does not necessarily happen when it is under a heavy load. When it happens, the laptop suddenly shuts down and the screen suddenly goes black. I have to wait about 5 to 10 minutes for it to be willing to turn back on again. This happens one to three times a day, and it is completely unpredictable. Below is a graph of various temperatures up until the point when it shuts down. None of these temperatures are high enough for me to suspect that this issue is caused by overheating. I would really appreciate it if anyone had any insight into why these random shutdowns are happening. Thanks!