[all variants] Low graphics mode and failure to reconfigure graphics

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http://ubuntuforums.org – An older computer in our house has been running Lubuntu for a while now, on an Intel Pentium 4 processor with 512MB of RAM. I's my father's computer that I setup and maintain for him but recently I've hit a snag. Every time I boot it, it will boot normally at first and show the Xubuntu (it also has Xubuntu) startup screen but then it almost immediately flashes to a menu on an all black background telling me that it's running in low graphics mode, and that my "Screen, graphics card, and input settings were not detected correctly". 'Enter' presses "Okay", and 'Escape' takes m (Hardware)