You are correct that you probably have a problem with your IDE cable. It's probably the "badly crimped cable" issue. Contact support and have them send you a new cable. You can install it yourself without voiding your warranty.
About the jumpers : if your mk2a only got ONE drive, there's no need for jumpers. If there are TWO drives the slave drive has to have a jumper on it to configure it to slave. (at least this is so with IBM drives, bu tI suspect it is the same with other brands)