|The correct end connector on a 3 connector 80 wire IDE data cable must go to the mboard header or controller card header - usually it's blue, but in any case it's the one farther from the middle connector. |
Some IDE drives, e.g. many Western Digital models, have two ways they can be set to Master - e.g. Master, single, for when they are by themself on a data cable, and Master, with slave, for when they are on a data cable with another drive set as slave. That must be correct for the situation.
It is common to un-intentionally damage IDE data cables, especially while removing them - the 80 wire ones are more likely to be damaged. What usually happens is the cable is ripped at either edge and the wires there are either damaged or severed, often right at a connector or under it's cable clamp there, where it's hard to see - if a wire is severed but it's ends are touching, the connection is intermittent, rather than being reliable.
Another common thing is for the data cable to be separated from the connector contacts a bit after you have removed a cable - there should be no gap between the data cable and the connector - if there is press the cable against the connector to eliminate the gap.
80 wire data cables are also easily damaged at either edge if the cable is sharply creased at a fold in the cable.
Try another data cable if in doubt.
There are some really old main chipsets that required you install IDE hard and optical drives on separate channels for the best performance, but it does not make any difference with modern mboards whether you have two IDE drives on the same data cable or by themselves - the cpu only accesses one drive at a time.