Why does my MacBook randomly shutdown?

Apparently, there was a design fault with the heatsink in the first generation of MacBook and that's what you're experiencing: the system gets hot enough and shuts down so it doesn't fry any circuitry. So in a weird sort of way, the shutdown is better than the alternative, but I can imagine how incredibly annoying it would be to constantly live under the threat of losing work or worse.

Fortunately, there's a well-known fix that Apple can apply to your MacBook which involves swapping out the heatsink with another heatsink. They wrote about the shutdown problem in what could possibly be the world's shortest knowledgebase article on the site: MacBook: Shuts down intermittently.

Their suggestion? Contact AppleCare for help. Or do what I do and call 800-SOS-APPL and schedule a pickup and repair over the phone.

Note that it's possible that MacBooks purchased today could still have this heatsink problem, and the way to test it is to push the device and see if you can get it to overheat. Here's one way that the folks at MacFixIt suggest:

1. Open Applications --> Utilities --> Terminal.
2. Type in the following command: yes > /dev/null & followed by Return. It'll look like this:
   $ yes > /dev/null &
   [1] 9881
3. Now type in the command a few more times and you'll have a number of processor-intensive commands slamming along in the background.

It should take no more than 15 minutes for your MacBook to either shutdown or demonstrate that you aren't plagued by the intermittent shutdown problem. If you're okay, then type in kill %1 %2 %3 for as many jobs as you started up (e.g., what I'm showing would work if you started three jobs. If you did four, add "%4" too).

The Apple service document for this problem explains to the technicians that: "The new heatsink part is now available for order in GSX and should ship later this week: 076-1243 Heatsink Kit, with Sponge, 1.0 mm Conn The MacBook (13-inch) Service Manual has been updated with this information and is available via links on AppleCare Service Source."

SO now you know. Get that heat sink fixed and enjoy that sweet little laptop! Me? I want one, but I'm waiting until the tablet form-factor MacBook is released... :-)