Powerbook g4 boot up problems

Hello,

my mother recently gave me my fathers old computer. it was a g4. i was excited to use it, since i've heard such great things about imacs...
unfortunately, i can't even to get it to boot up!

when i plug it in, it immediately turns on and shows a white screen with an apple in the middle, with a small circular loading/waiting bar underneath. and that's it! the waiting bar just goes around and around in circles and nothing happens. the hard drive does seem to engage and rumbles, but then stops after a few secs...

i took out the battery, i tried resetting pram(?) based on advice i gleaned from other people having problems and posting on forums, etc., but their problem all seemed to be either bad batteries, power supply etc... that doesn't seem to be the case with this one. i don't even hear a chime.

is there any way to actually boot up into a "safe mode" or something similar?