Sounds like something physically went wrong with your hard drive. So lets try to fix the drive.
1. Quit all programs.
2. Boot into
Single-User Mode and run
fsck -fy. Keep running the same command until it's gives all clear. After you are satisfied and want to boot back into OS X normal mode just type the command: reboot
3. Another way you could install
AppleJack and run it's routines instead of fsck-fy instead in single-User mode. It could do more than just fsck-fy could.
4. Buy IMHO the best disk fixer for OS X called
Disk Warrior. This program has fixed my personal bacon so many times now I always use this program about once every four months, for preventive maintenance.
5. You hard drive may not be fixable. So boot in to your backup clone (Time Machine or a program like
Carbon Copy Cloner) (since you can boot into cloned externals in OS X) and
replace the hard drive and clone back to it.
Hopefully you can recover but I can't stress hard enough to ANY computer user (Mac users also) that having multiple backups is necessary and when you hard drive fails (all hard drives will fail at any time during it's lifetime) and you have no one to blame but yourself when the hard drive starts dying.
I hope that you are able to get your data back. Good Luck.