Make sure you update to latest initramfs-tools. Reboot, and wait several minutes to see if busybox drops to a shell.
I'd be willing to bet this is an old bug in the installer. To see, edit /boot/grub/menu.lst, find the line that starts "# kopt_2_6 = " and delete it, then run 'sudo update-grub'. Rebooting should resolve the issue. ** Changed in: linux-meta (Ubuntu) Status: Unconfirmed => Fix Released -- kernel 2.6.20-3.4 not bootable on amd64 https://launchpad.net/bugs/77847 -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs