Creo que el "unhide" tienes que hacerlo directamente sobre el sistema operativo y no desde Dolphin, prueba a montarla antes de nada a ver si eso la restaura.
Si no, puedes intentar si estos pasos funcionan:
Start a Terminal, Konsole, xterm, or other text-mode shell
Type "sudo fdisk /dev/sda"
Type "p" to verify that you're working on the correct disk.
Type "t"
Type the number of a partition whose type you want to change
Type the new partition type code. To unhide a 0x1c partition, it should be changed to 0x0c. You can omit the "0x" part and just type "0c" or even just "c".
Repeat steps 4-6 for any additional partitions whose codes you want to change.
Type "p" to check that you've made the correct changes.
Type "w" to save your changes.
Saludos
