iBook won't restart or shutdown

Hi, was wondering if anyone could offer any advice, when i try to shtdown or restart my ibook my dock and desktop icons vanish like normal but then nothing happens, it stays on with the desktop wallpaper there and fails to closedown. Why is this?! Shutting down my holding down the power button feels like it's doing damage.

It's OS X 10.4.6 btw

Holding the power button down to shut off your computer is not going to damage it.
Since you are only running 10.4.6, the first thing I would suggest doing is updating the OS to the current version, 10.4.8.
After that, then try downloading and running a tool like MacJanitor or OnyX to clean out your caches and such.