Previous Shutdown Cause: 3

Does anyone have any clue what this means? I don't understand computer-speak. My MacBook shuts down unexpectedly if it is left inactive for more than a couple minutes--sometimes the fan is running, most of the time it's not. Sometimes there are active applications, sometimes there aren't. Sometimes it's plugged into the adapter, sometimes it's on battery. Nothing is consistent except the fact that I can't walk away for 2 minutes to answer the phone or get a snack without returning to a shutdown computer.

Help!

Thanks.

Here's what the system console says when I search for the term shutdown:

Sep 5 14:30:56 localhost kernel[0]: Previous Shutdown Cause: 3
Sep 5 15:13:18 localhost kernel[0]: Previous Shutdown Cause: 3
Sep 6 09:16:26 localhost kernel[0]: Previous Shutdown Cause: 3
Sep 6 09:17:58 localhost kernel[0]: Previous Shutdown Cause: 3
Sep 6 12:42:08 localhost kernel[0]: Previous Shutdown Cause: 3

Here are my specs:
Model Name: Mac
Model Identifier: MacBook2,1
Processor Name: Intel Core 2 Duo
Processor Speed: 2.16 GHz
Number Of Processors: 1
Total Number Of Cores: 2
L2 Cache (per processor): 4 MB
Memory: 1 GB
Bus Speed: 667 MHz
Boot ROM Version: MB21.00A5.B06
SMC Version: 1.17f0

My Macbook was purchased in mid August 2007, and it runs 10.4.10, so the earlier firmware problems shouldn't be the problem. I would call Apple Support, but I'm in the Middle East, so wherever I call will be long distance. I'm trying to resolve this problem independently. It will be a tremendous inconvenience if I have to travel to Rosh Haayyin (near Tel Aviv) to take it to an authorized repair location...or worse ship it back to the U.S.