Recovery corrupted file from external hard disk

try error checking on the ext hdd. right click on the drive from 'my computer' > 'properties' > 'tools' > click 'check now'.
you can restart your pc and reconnect the ext hdd.
piriform's recuva is a free data recovery program.

Data loss due to hard drive crashes or other logical errors may happen. Be prepared for the worst with the best. Use Kernel for Windows Disk Recovery and be assured of your data even if the partitions are lost. Kernel is competent to recover files from any windows file system.

Please verify 2 things 1) If the storage device shows up in my computer and is accessible 2) If the storage device shows up in Disk Management but is in the "unallocated" state.

Does the drive show up in my computer

If yes are you able to access it? If no why not? what is the error message given.

Does the drive show up in disk management?

If the drive shows up in disk management but it says "unallocated" then the partition will have to be recovered.

Data Recovery uses specialized hardware-based data recovery tools, coupled with years of experience, to recover data from dead and dying hard drives -- | handsofsupport.com

Losing those important files are really pain in the ass. I suggest using a recovery software. If your not familiar with it, a nice simple guide from recoveringtips.com would come in handy.

Here is the specific link of the post:

http://recoveringtips.com/How-to-recover-files-from-cor...