|In theory IDE cables can be cable select only, but I've never encountered one.|
However, 80 wire data cables MUST have the proper end connector connected to the IDE header on the mboard or on a drive controller card in a slot - usually that's blue, but in any case, it's the one on the end farther from the middle connector.
Cable select and Master / Slave uses at least two different wires in the data cable.
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.