Won't install Java

One day my computer came on and said i no longer had an operating system.  So i reinstalled.  Since then I have been unable to install Java and almost anything else.  I get an error message saying all the nessecary files could not be found, doesnt matter if i go direct to the site, use the terminal, package manager , none of it works.  I have an older machine , a pIII with only ten g  but it did work for a time.  any thoughts?