That green square follows me everywhere. I can cycle thru the main menu items, but as soon as I try to enter any music folder (Music or SD card sections), it freezes completely and I have to restart it, so I can’t play any music.
The green square appears only in the menu. It doesn’t appear, for example, during the SanDisk logo when booting.
If that doesn’t help, you can also try manually re-installing the firmware. Formatting is the 3rd option. Note that formatting will erase any files (music, sudiobooks, etc.) that you have on it, so you would have to re-transfer those afterwards.
There’s really nothing else you can do. If none of these 3 options work, then I suggest calling/contacting SanDisk about a possible warranty replacement.