If FDISK isn't seeing your drive, then something has actually failed: Either the HD itself has quit, or the cable is funky, or the connection is bad. If you change positions on the ribbon cable, you'll probably need to reset a jumper on the back of the drive that determines whether it is the Master or Slave conneciton. (Master is on the END of the cable, and slave is in the MIDDLE of the cable).

But, try reseating the connections first (check the power connector to the HD as well), then if that doesn't work, try a new cable, if still no go, the drive may have actually failed.

You'll have to be able to FDISK to get any further with the drive regardless...