problems with pc

start up computer it tells me disk boot failure insert system disk and press enter i put winxp pro in then go to windows menu and go to repair and it tells me the path or file is specified is not valid... and if i go to setup windows xp pro and it says the following are lists of partitions and unpartioned space on this computer to scroll and pick one but where there supposed to be it gives me setup cannot access this disk ..
any help would be appreciated thanks