Non system disk or disk error replace and strike any key when ready

my computer was working fine yesterday and when I woke up this morn It read non-system disk or disk error. I tryed to reboot it an it rebooted but it went back to the same thing. When I press any key it just pops rite back up. It said disk failure I just looked at it and its a compaq not a dell omg sombdy help me please I dont knw alot about computers but im willing to learn.