If you have the whole old drive then you probably still have the hand history files - these are likely to be in the "PokerTracker 3\Processed" folder.
If so you can copy them to your new computer and import them into your new database.
You may be able to recover the postgres databases from the postgres\data folder too.
This guide explains how to reconnect to an existing data folder:
How to reinstall Postgres.
See also the How To section of the
Database / Postgres FAQ for further links.