Hi Reto,

I have found that if the players lock up in some way a very long press on the on/off button can reset them. Worth a try anyway.

Installing Rockbox is not difficult. All you need to do is download the installer (https://www.rockbox.org/download/) and follow the instructions on the site. It's years since I have done it but I remember that it was very straightforward at the time. You don't need to dismantle the player in any way.

I found the original SanDisk software was very poor but Rockbox has provided all the features I need for many years.

Dave