Lately (since I installed Tiger), my powerbook 15" G4 will not shut-down, sleep, restart or log off via software instructions. It will only sleep if I close it. It will only shut-down if I hold the power button down.
I and many others had the same problem. The solution is to remove all start up items and re boot. You can then add them back one by one till you come to the one which is causing the problem. Any thing from Norton should be trashed.