First, what do you mean "blue screen and cursor"? If it's a gray "fine checkerboard pattern" with a cursor you can move, it MIGHT be just that you don't have a boot device in it. Try holding Command-Option-X-O while turning it on and see if it boots to the ROM partition. (The original "Macintosh Classic" is the only Mac with a bootable ROM drive - no other Mac has this, not even the Classic II.)