MyBook used on Mac, no longer seen by PC

We were using a MyBook Essential on a PC Desktop. Also to back up my sons’ laptop computers.  One of my sons bought a Mac Book Pro, and we successfully transferred his PC data to the Mac.  During this process, the Mac automatically made an encrypted backup on the drive.  Now the drive is not recognized by the PC. (Plugging in the USB on the PC gives an audible flourish, but the icon never appears on MyComputer).  On the Mac, the folders are there, but they are newly password protected (the data was not password protected on the PC) and no obvious password works.  So close yet so far.  Just enough to know the data’s still there, but not able to get at it on either computer/OS.

Try posting and screen shot of the error you are getting

what software did you use for the backup?