Unity worked perfectly in my laptop before. However, today when I hard rebooted my laptop, there's something like disk/drive error detect before the login screen. I waited until the disk/drive check finished and then login. Now there's a pop up saying: "It seems that you do not have the hardware required to run Unity. Please choose Ubuntu Classic at the login screen ...", then Unity did not work anymore. It turned back to Ubuntu Classic automatically, and I could not use any effect.
Any idea about what happened? How can I get it back? It happened the same before, and it turned into worse after that and I have to re-install Ubuntu. That's why I'm so desperate. Please help.
lspci | grep VGA returns:
Intel Corporation Mobile 4 Series Chipset Integrated Graphics Controller.