My G4 PowerBook (Aluminium 15" 1.67Ghz, A1104) keeps putting itself to sleep at odd times. This is without a main battery in place, and a dead PRAM battery, both of which I'm waiting to replace. When I wake it up, it tries to power up, HD spins, but then goes back to sleep without even the screen coming on. I can do this like 5 or 6 times, and then eventually it wakes up and stays awake. For a while. For the first time today it wouldn't actually even start up from a total shutdown 2 minutes revious. It was just dead. After about the 6th press of the power button it started up. At first I thought it was a faulty power lead (though the green light on it never flickers on/off to show loss of power). So I've borrowed a mates lead, and although it seems to have reduced the sleeping problem, it's still happening regularly. Any ideas????