I am running Ubuntu 12.04 on my laptop and my graphic card is NVIDIA GeForce 8400M GS. I was watching a video, when my laptop all of a sudden rebooted. It couldn't finish the reboot properly and got stuck with a black screen and the commands that check different parts of the system. My monitor does not show letters properly (e.g., continue reads c t ue). I tried using the Grub loader to revert back to a previous kernel. Now, I have the GUI but the resolution is awful and there are so many strip purple vertical lines on my monitor. I also tried purging NVIDIA driver and reinstalling the driver. It did not change anything. It is worth noting that even the DELL window at the very beginning of the boot doesn't have a perfect picture and there are so many missing pixels. I'm using an external monitor, tried disconnecting that and it didn't help. My laptop screen is also weird. Any help with regard to this will be highly appreciated. Thank you.