So I've got a vintage PowerBook G4 (PowerBook 1,6). And, every time I travel with it (without the power cord), it unexpectedly shuts down. When I try to start it back up, it does a Kernel Panic once the Apple Logo comes onscreen. After I go into single-user-mode and do a file system check, it seems to be alright. The PowerBook is running Leopard. Is this a hardware or a software issue?