Why can't I login after a hard reset?

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http://askubuntu.com – Ubuntu boots normal, and I can even login in terminal at any TTY (tt1 ~ tty6), but not in Graphical mode. This happened after a power-suspend. As I was trying to resume after the system suspended due to a running low battery, and wasn't getting my Ubuntu back, I made a hard reset (power button). I could not login anymore from that moment on. (HowTos)