This could be a disk detection error, especially after an unsecured shutdown or a damaged disk.
Workaround:
1. When selecting the startup item, select the first item, such as:
Ubuntu 8.04kernl.2.6.22-16-generic
2, press E to enter the editing state, in the last few lines see load Kernel command, similar to this:
/boot/vmlinuz-2.6.22-16-generic Root=uuid=xxxxxro Quiet Splash
3. Replace "quiet Splash" with "all_generic_ide" at this time, then press CTRL + X to run.
4, the system will enter the automatic detection state, if the shutdown error, may start failure and the following prompt:
Fsck exited with status code 4
5, then try to use the following repair:
Fsck-y/dev/sda6
6, where sda* is your system's partition, can be viewed via sudo fdisk-l
At this point, the system will start successfully ~
Linux Startup issues BusyBox vx.x.xx built-in shell