[PROBLEM] Stuck on black screen at boot

[ilikexbian]

Hi,

After doing an upgrade via ssh, my system was going (automatically) for a reboot. After that, it did not came back.
I tried to restart it by disconnecting the power source, but I only get a black screen.

The only problem I had, was that I had no free space left. So maybe something is corrupted. However, I think it is strange nothing happens (no logo, no text message) on boot. Because of the btrfs that is being used, I cannot use my Linux Mint install to investigate the problems, right?

Do you got any clue what's going on and how I can solve it?
I have a RPi 2.