Well, you're about right, yes, only X and Y are switched places.
So, yes, I have W and Y on my computer originally. X was a primary disc in another computer and did not work (could not start the OS). Then I plugged this X disc into my computer and backed up the important files all right. Then I wanted to reinstall the OS of X disc and booted it as primary (just switched off the W disc and reswitched X's jumpers).
At the beginning of the reinstalling/upgrading I found out that there was not enough space in X disc for an OS, so I decided to reload it as a slave disc once more and delete some files, but I had problems loading the W disc as primary (if the all discs were switched on, it tried to boot from X and froze, if I switched off X and booted from W and then tried to switch it back on (while the OS was running), it could not read the disc). I suppose that somewhere here it went wrong...
Anyway (having not yet discovered that I can set which one of the hard drives is booted from in the BIOS) I gave up deleting the files and decided that as I have a back up of the user files, I can as well reformat X and do a fresh OS install. At that point I reformatted the X disc but after that "Windows" setup informed me that the X disc was curropt, cannot be restored and that setup cannot continue.
Now, I disconnected disc X and boot from W. At first I still had booting problems as I could not boot with Y connected (as it tried to boot from it, but it doesn't have a OS installed). I'm not sure wether the system - whatever system it is at this point - could see it as the old Y disc or was taking it as the already disconnected X disc (which
had OS installed on it, only corrupt). When I disconnected Y, it booted from W all right. Then I discovered where in BIOS I could set which disc to boot from, and I could boot with both discs connected. Unfortunately, it didn't see the Y disc correctly anymore.
I too hope that someone can help... I cannot afford to pay for professional data recovery company services.