You don't have those files backed up anywhere else? - not wise. Precious files should be kept on at least two drives, not just one.
Why? Because all hard drives will fail sooner or later. It's just a matter of "when", not "if".
The error could mean a hardware problem with the drive, but try it in a different PC just in case it's your PC that's causing the error. If possible, copy your files to another location if a different PC can read it.
I would then test the drive with "Seagate SeaTools for Windows" which can test any hard drive brand. Click "Downloads" on this page: http://www.seagate.com/support/downloads/seatools/