Mac won't boot up need help!!?

I have a PowerBook G4 that i received from a friend so i do not have any OS installation disk. It was running OS X Tiger and i was trying to install leopard onto it from a .dmg file. I tried restarting the computer and it will go into the screen where the apple would be but shows a folder with a question mark which i found is a hard drive problem after that the screen will flash black with 2 lines of words on it. I need help getting this started please help!! Once again i have no Operating System installation disk to use and i have tried many start up tricks help!!!!!!!!