Disk boot failure message harddrive new

Hello,
our computer has an ASUS P4B533 motherboard with a pentium 4. The hard drive and video card is new. Everything has been running fine until last week when "disk boot failure, insert system disk and press enter" started showing up. Windows is functioning fine because our neighbor got us into it through the backdoor. If you don't turn the computer off it is fine, but we always get "disk boot failure..." upon restart and inserting the disk does no good. Is our prossessor or motherboard dying?