I have a PowerBook 3400 running OS 8.1 with 48 meg RAM and VM on. It acts as if it has some kind of short in the battery. Everynow and then when I running on the battery the computer shuts down without warning. Usually I can start back up with no problem. Today it did it twice within a few minutes of each other. The second time it would not restart. I tried holding down the reset button in the back for several seconds but it still wouldn't start. As soon as I plugged in the power adapter, I heard the chime and it started fine. The battery showed that it still had more than 75% of its charge. This only happens when I am running on the batterey and the battery always shows that it has plenty of juice left in it. It does not happen often enough for me to determine any cause, but it I believe I have always had my hands on the keyboard or pad when it happens. What causes this?