17" Powerbook G4 must sit for hours to boot
If it chimes, but then takes a long time to boot, you might be able to figure out what it's doing by booting into "verbose mode":


Hit the power button to start it
Immediately hold down Command-V


This will change the boot screen to a text scroll from the kernel putting out messages as it boots. That might show you if it's getting stuck on something.

You might have to do it a few times to be sure. If the disk drive is going south, that might show up as drivers are whatnot having a hard time loading. If it seems to be a different driver each time, or a lot of them, it's probably the drive.