Are you running 2 Windows installations? Or did you format the old drive?
Did you reinstall Postgres and HM2 on the new drive?
Please see this FAQ to move your database to another drive. Please note this is an advanced article and we do not provide support for this method if you encounter issues but at the request of users we decided to make a FAQ for those who felt confident enough to try this method.
Hold'Em Manager 2 FAQs - Poker Software :: Move Database to Another Hard Drive or Partition