The problem with Microsoft error codes is that they are very generic. This issue may or may not be possible to fix. The only way to see is to try one of the methods already spoken about.
FYI,
this was the 3rd hit on google search for UNMOUNTABLE_BOOT_VOLUME
GetDataBack (for ntfs or fat32) is a nice app for attempting to recover lost, deleted, or mangled files. I have had issues with GDB locking up on bad sectors. In those cases, I've found
rStudio to handle the bad sectors more effectively by simply skipping over them instead of trying for 4 hours to recover unrecoverable data in that one sector, only to repeat the process several more times with other bad sectors. At least you can recover some of your data instead of losing it all.
I was told a story by an acquaintence who is a computer shop repair tech. He told me once he was able to recover data off of a lady's harddrive where the motor had given up the ghost. He claims to have mounted a drill or router onto the harddrive spindle, found the correct RPM on the drill or router, and was able to allow the computer to read the drive. Supposedly he was able to recover more than 50% of the lady's data off the harddrive. I don't put much faith into this story though.
Let this thread be a lesson to have working data backups, either through one or more external harddrives, online backup services, server with redundant harddrives plus external harddrives, etc.