If you are unable to boot into your Ubuntu/Kubuntu/Xubuntu system, and it shows you the Busybox terminal, try run the fsck utility on all partition, especially the partition that you install your system. Here are the easy steps on how to do this:

1. Boot to your system with your Ubuntu/Kubuntu/Xubuntu Live CD. Run the partition manager software (GParted) to check on which partition you had your system installed (1). Take note of the partition file system (2). In my case, I’ve installed my system on /dev/sda1 with ext3 file system.