Disc Boot Failure means it can't find an operating system - Windows ME
If it has a floppy drive make sure that is it empty and no floppy disc in.
Ditto for the CD drive.
Remove floppy disc and CD if they were in, then reboot PC
If it still gives the Disc Boot Failure message then it is the Harddrive not working.
Switch off the pc and unplug the wall plug then:
Take the side off the pc tower and reseat cables to Harddrive (unplug the connections and then plug them back in again)
Switch on pc and boot up and see if that fixes it.