I did a clean installation of ubuntu 12.04 from a usb stick. After installation, first boot was normal so i logged in installed some apps and lenses and downloaded updates. When I rebooted to install updates after bios screen it said boot manager is missing, press alt+ctrl+del to restart. so how can i repair/install mbr? thanx
The boot manager for Ubuntu, GRUB2, was probably broken when you were installing updates. Try using Boot Repair to fix it. First boot to the Ubuntu live CD. Open a terminal window and run the following code to install and run boot repair:
Then follow the instructions and options in the program to repair your boot.
You can visit http://www.howtogeek.com/114884/how-to-repair-grub2-when-ubuntu-wont-boot/ for more information.