Unable to start Ubuntu 12.04. The system is running in low-graphics

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http://askubuntu.com – I am a newbie to Ubuntu. I installed Ubuntu 12.04 using a USB Stick and it was running all fine for a few weeks and this error popped up. According to one of my friend, the best way was to re-install Ubuntu. Being a non i thought the same too and after the second install it happened again, but only this time was much quicker in 3 days. and i don't want to re-install Ubuntu every time this happens. I am a complete newbie to Linux which means that i stuck at terminal. I know there are other people who fixed this issue in this very same forum, but unfortunately the answers provided just look lik (HowTos)