Macbook shuts down when closed?

[wightstraker]

My sister has a first generation Macbook (black, 2GHz, running 10.5.4) with a particularly frustrating problem: every time she closes it, rather than go to sleep, it simply shuts down.

I've been digging through the forums and have noticed a lot of problems involving macbooks shutting down at unwanted times, but so far I haven't encountered another example of this particular snafu.

Any idea what's going on here? Is their an obvious fix for this (firmware patch, .22LR autoloader?), or should she take her laptop in to Apple?

Thanks in advance for your help.