Rule Number 1: Don't sweat the small stuff. Rule Number 2: Everything is the small stuff. Data recovery can be simple, erasing files may be more difficult. Recover deleted files and lost partitions, while maintaining security with low-level format.
Simple data recovery software usually does the trick, but recovery from drives that can not power up can only be performed by trained recovery engineers. These engineers will move your damaged drive(s) into the clean room, where their equipment can copy a duplicate drive.
Any write operation can overwrite deleted files for good. So, in case of suspected problems: don't write anything to data drive, don't run any disk utilities such as chkdsk and defragmenters, and don't reboot your computer.