When booking up, a symbol that looks lik...

try holding down command(apple key), option, p, and r after the chime this should reset the non volatile ram and the startup disk, cache, etc. if that doesn't work restart holding down command option o f after the first chime when it loads to a white screen type the command "reset-all" exactly like that without quotation marks and hit enter if the computer doesn't restart type "reboot" or maybe "reboot- now" or "reboot now" I can't remember exactly but you can try them all and if that doesn't work with the osx cd hold down the c key (option c on some earlier models) or option key after the first chime the c key will boot straight to cd option will give you a choice between cd hard disks or network boot select cd and press the arrow underneath it after loaded from the cd you will see options at the very top of the screen like you would see in the finder in one of the drop down menus I think it is utilities it will have Disk Utility open that select the disk on the left and go to the repair screen by selecting the appropriate tab at the top of the center box then at the bottom right click the repair disk tab if it cannot be repaired you must reinstall the system NOTE:the hard drive may be bad in which case you will not be able to reinstall unless you replace the drive however if you cannot boot to the cd then you more than likely have a serious hardware failure and will have to bring the computer to be serviced although on that old of a unit it may just be time for an upgrade if that is the case
good luck and best wishes P.S.-don't forget to rate me