[Solved] SATA cable problem

You start with "For a time now ..." This sounds like an intermittent problem that has become worse until you fixed it.

The most common problem I've encountered inside computers is just like this. Over time the metal contacts in connectors build up a fine layer of metal oxide on their surfaces, leading to poor connections. At first this is intermittent, but eventually it becomes permanent. The fix is surprisingly easy. If you simply disconnect the cable and then re-connect (preferably several times) that action often will scrub the oxide layer off and leave you with good contacts again. So when this happens to me I shut down and disconnect from power, open the case, and go through the entire innards. I'll disconnect / re-connect every cable I can find at both ends.

Just be careful of a few things. First is a general principle: DON"T FORCE IT! Connectors RARELY are so stiff you must pull hard. If it seems tough to disconnect, check closely to see if it is some kind of locking connector with a little tab you must press to free it. It"s especially true when you re-connect: if you have to push it in really hard, don't!. Look more carefully and be sure the pieces are aligned correctly so they fit smoothly and easily. Next is to be gentle enough that you don't hit or twist something hard enough to break it. And lastly, watch to be sure you don't loosen something else while you are working on the current cable, or you might create a loose connection you don't know about. And if it does not work after all your "cleaning" actions, look closely again to see if there is an unrecognized loose connector. Oh, and a last rule: do this one cable and one end at a time. Last thing you need is five cable ends loose so you risk plugging two or three into the wrong places!