I've just upgraded my Gnome version, using the gnome3-staging PPA. Since it is still a little buggy, I've done a ppa-purge to come back to the 3.14 version shipped with Ubuntu 15.04.
After a shutdown, the PC won't reboot at all. After the Grub, what I only get is a black screen. I tried the recovery mode, and now I can see the kernel logs while the PC is booting but, the recovery menu is never displayed: I have no errors in the console, but suddenly the scrolling stops, and nothing more happens. No stdin, no menu. The last displayed line is something like "Btrfs: Found SSD devices, activated SSD mode.".
Fortunately, I also have a Debian on my PC. I tried to mount my Ubuntu partition to read the logs. Unfortunately, the kernel used by my Debian is too old to read this Btrfs version.
Do I have to reinstall Ubuntu? :/