Hi i got a buffalo tb external hardrive and the pc

It is probable that since the transfer did not complete, the data on the external drive will be corrupt.

Uninstall the external drive then reinstall and format the ext drive.

You should then be able to begin the data transfer process again.

It just sounds like bad luck that your pc froze mid transfer.
When you try again, do not use the pc for any other uses until the transfer has completed.

Regards and let me know if this works for you.