Black screen while boot - Can only boot in Recovery mode

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http://askubuntu.com – System : Ubuntu 12.04 with Gnome. 64 bit. Today, when I was adjusting the display driver, the system started behaving abnormally, first the menu was missing (both in Gnome & Unity) and sometimes the display was coming with a purple tinge. I was trying to remove the Nvidia driver, then there was a power failure and I was completely messed up. There was some issue of Kernel Panic also. But, somehow it got partly corrected and now I am able to login to the system in recovery mode. If I select the normal boot option, I am getting a black screen after the iniitial purple screen. With recovery (HowTos)