Being a "Mystic" CC means it has a LC575 motherboard correct?

The only things I can think of would be a conflict between the HD and CD Drive, or the CD is scratched. You could try booting without any HD and see if it works or boot from a different disc.

Hope this helps.

Edit: I found this, maybe there's something useful there.

http://colourclassicfaq.com/mobo/mystic.shtml