All of a sudden my Audya doesn´t play most of its audio drums. Still some of them are doing all right, but the rest don´t work. Not very long ago I installed the latest OS, but - as far as I remember - everything seemed to be all right afterwards. So what might have happened? And more important - how could this problem be solved as quick as possible, because I need the keyboard urgently! Thanks for all answers.
P.S.: Restarting didn´t help.

Have you any problem with disk ( hd or ssd in your audya) . Connect audya and computer with usb cable and check is there some errors.I hope it is not error in the drive.

That´s what I hope, too. I´ll have a closer look today.
Moreover I conceived the following idea: Two weeks ago I made a complete backup. Might it have happened that some audio drums had been moved instead of only being copied? I think that could be a reasonable explanation, couldn´t it? And wouldn´t a solution be easy then - I´d just have to copy the audio drum folder from my computer onto the Audya´s drive. What do you think?

Correct .....