Internal hard disk problem

Whenever i starts working on my desktop computer,
Sometimes it normally starts
but
sometimes it shows error message like
"Reboot and select proper boot device or
Insert media in selected boot device and press a key....."

Sometimes hard drives works properly
But
Sometimes it suddenly stops working with a ghrrrrrr sound.... And start working after some time..... And repetition goes on

Its very annoying.... Plz help