You'll only know the exact condition by running the manufacturer's HD Diagnostic extended CD scan with all other HD's unplugged as I advised in first post, although you can read SMART data at any time using CrystalDiskInfo - Software

If data is irreplaceable then perhaps you should use a rescue disk as described in Step 9 of Troubleshooting Windows 7 Failure to Start so that it's the DVD or CD which is doing the work.