Imac G4 boot-up problems

My son mistakenly tried to install an update on the 1.25 ghz Imac G4 he uses. Now it just boots up but goes as far as the Apple logo and spinning wheel and no further. I tried booting up in safe mode (pressing the shift key after the boot-up chime) but then it gives me a blue screen with the pointer that I can move around with the mouse and that's it, no icons of any sort.

I don't have the original discs or a copy of Leopard, which is what's on there now.

Any suggestions?

via ehMac.ca http://ift.tt/VLegPv