My Toshiba hard drive doesn't work on Windows machines
If you're using Time Machine on the disk, the disk is Mac OS Extended formatted which can't be read by Windows without additional software.

You can use the Boot Camp drivers which integrates HFS read/write into Explorer.


http://support.apple.com/kb/DL830


Alternatively, you can use HFSExplorer:


  HFSExplorer is an application that can read Mac-formatted hard disks and disk images.
  It can read the file systems HFS (Mac OS Standard), HFS+ (Mac OS Extended) and HFSX (Mac OS Extended with case sensitive file names).