T22 problem: sudden black screen

[baobab]

I have a T22 that is just (May'04) off warranty. The machine has been problematic: 2 new hard drives, 2 new keyboard bezels, a new backlight and finally a new motherboard. All were covered under warranty, and things have been running smoothly since the motherboard was replaced late last year.

Until today. Today the machine went to a sudden black screen four times, each time after being moved (i.e. put down). This appears to be a sudden shut down rather than the screen turning off, since the ultrabay light goes off too. It's possible that relatively sudden or jerky movement makes this happen... moving it slowly doesn't seem to have the same effect, but the same type of motion in the past has never caused a problem. Hitting the power button powers up into a normal W2K boot sequence, and unlike the blue-screen crashes I'm so familiar with, it seems to retain its short term memory for web browser history, etc.
I've defragged and checked the hard drive, and it appears to be healthy. Also, the battery is in and functioning, so it's not a simple matter of a loose power cord.

Any thoughts on what may be causing the black screen shutdown or how to fix it? I'm not quite ready to spring for a new machine, though I will probably get a T4x later this year or early next year.

thanks.