One useful tool is Windows XP's built-in system restore tool. If a recent system restore point exists you can go back to that point in time and recover your database (note: this will erase changes made since the restore point). To use system restore go to Start | All Programs | Accessories | System Tools | System Restore. Or you can manually create new invoices. If you made a recent backup of your database you can restore that from the File | Restore Database option.