Macbook Pro mysterious random shut down

My Macbook Pro is randomly shutting itself off. It's a 15" Intel Duo Core running on Leopard. I always update my software and treat my computer like a baby. My battery is only 1 year old, but the computer is from 2006. For some unknown reason, these shutdowns have started a month ago.

There is no pattern and there is no setting that it lasts longer or shorter than the other. I've tried on battery power only, adapter + battery, and even no battery. It's been on my lap, on my bed, and on my desk. All led to a random shutdown. I brought it in to the Genius Bar but they said there was no problem (but could be the logic board). Brought it to a third party repair shop overnight and they said it passed every test and it never shut off at all the whole 24 hours.

I am no longer under warranty (as of 4 months ago...) so I am lost. I've read a number of forums and found similar (but not the same) issues with younger macs who just bring them in for repair at Apple.

I can't afford to pay full for a new computer and no one will buy a computer if it just shuts off unannounced.

What ghost haunts my computer?

How about trying the Combo updater see if that helps;

Apple - Downloads - Mac OS X Updates - Mac OS X 10.5.8 Combo Update

Next choice would be hunting for .plist - but not sure which one yet.

To bdoyle:

Random shutdowns can be difficult to troubleshoot, however, there are several most often causes:

1. Overheating. (Check your machine's fans. Make sure they're both working the way they're supposed to.) Open up your machine and blow the dust out of it with canned air.

2. Power Supply. (Intermittent component or poor regulation)

There are other reasons also, such as was mentioned to you. (logic board)
(bad memory)

Regards.

Any idea how to back up a mac book pro that keeps restarting?

I'm having the same problem. My macbook pro keeps restarting itself. It normally only stays on for a few minutes, then restarts. I brought it into the store, and they said its likely the logic board, but they cant guarantee that once they ship it out to be fixed, they wont do something with the hard drive. So I brought it back home and I need to back it up. The problem is that it won't stay on long enough for me to get my files. Any idea how I can get some of my files off of the computer if it keeps restarting? I know the guy mentioned there was another way to start the computer so I could hook it up to another mac and basically use my mac as an external hardrive and grab the files off of it. Also, is there any way to do this without another mac? Any help would be GREATLY appreciated! Thanks!