Howard P, that doesn't sound fun. There's not a whole lot you can really do if the system won't recognize the drive. I don't know how technical you are, but either you or a tech can move the drive to another system and see if it finds it. If it doesn't, it sounds like the drive may have died and it's time to see if your warranty is still good.
On a side note, I doubt Defraggler had anything directly to do with it. A bad one, but it sounds like a coincidence.