My NTFS formatted external Toshiba drive is unreadable since update to Yosemite OS X 10.10.1
Connect your HDD to Windows computer and check&amp;fix it (it is under properties of that drive).

After that reformat the drive to HFS+ if you want to use it with Time Machine.
NTFS is not supported filesystem for Time Machine why did you started to use it in the first place?