[ubuntu] "the system is running in low-graphics mode" + can not log in from a command line

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http://ubuntuforums.org – hi all! I'm sorry if this description is too long - I was not sure what was potentially important and what wasn't. I have an ubuntu 12.04 installed on lenovo x301. For a few days now, I get "the system is running in low-graphics mode" error (described here) when I try to boot. In my case, it is apparently due to the lack of free space left in my home directory (0 bytes free as of now). To free up some space, I first tried to boot up from livecd (as discussed here), but without success : "gksudo nautilus" did not work (some error messages appear when I try to install nau (Hardware)