I read through similar problems, but nothing I found solved my particular problem.
I used to run a dual boot WIn7/Ubuntu 14.04. I was in Windows when suddenly the screen froze. Cursor was still active but couldn't do anything within the OS (not even start task manager). So I tried a hard restart. Once it restarted I was met by the message:
operating system not found
Grub Rescue loads.
ls (hd0) (hd0,msdos1)
Then when I try
ls (hd0) ls (hd0-,msdos1)
File system unknown.
Any suggestions how to back into the OS without wiping the hard disk? There is some data, I really cannot lose.