Its always good to perform routine backups... you should do it too.
Usually the error message just means the file system is damaged and cannot be mounted for some reason (more commonly it is due to a corruption in the BOOT.INI file)... but... download the hard drive manufacturer's hard drive diagnostic utility and run it on the HDD to see if it is fine.
The Utimate Boot CD has the HDD diagnostic utilities on it too... it is a useful tool to have around...
http://www.ultimatebootcd.com/download.html