Powerbook hangs at "Login Window Starting"

I've got a 15" Powerbook G4 1.5Ghz and I am having trouble starting it up. Everytime that I start it, it hangs at the start up screen and has a progress bar that is almost full, but it says "Login Window Starting," and it just sits there forever. I just got my copy of OS X Tiger, figuring that I could do an upgrade with that and it should fix my problems. Well, it wont even install. It gets to the installation after holding the C button down at start up, and finishes saying that there was an error installing, and to please try again.

There's 9 GB free on the hard drive, but for some reason I can't get it to install. Any suggestions? Is there a "safe mode" type start up like on windows machines? I'm not very familiar with macs, I just switched over about a year ago, but have never encountered this type of situation. Please help!

Thanks in advance!

hey...did you ever figure this out? I am having the same problem right now...it sucks I'm starting to get fed up with mac because it's a new hard drive since my other one messed up...my sister has a pc laptop that is ancient and it is still in good condition...I've only had mine for 3 years. (powerbook g4, 768ram)

not sure what to do...I just turned it off (after 3 tries) hopefully it starts up normally when I get to it again.

If anyone out there knows what I can do...I've searched on here to find some stuff to do but tired to looking....the hardware test passed, I tried the shift key on start up thing....still no go.

HELP! someone! anyone!