You need to boot from a rescue or boot floppy. If you don't have on of these then you may be out of luck. If you do have one and it is your root filesystem that is corrupt then you will still be out of luck, Because if you shut down improperly youtake a risk of corrupting our file system, and most of the time the only way to fix it is to basically reformat, and then reinstall your lost files from a backup, but of course that is only helpfull if you have a good backup strategy. Your only hope may be to re-install the OS. Remember always use the proper shutdown procedure and make regular backups.
Paul