The real answer is , your screwed,
If you format a PC or a MAC and install windows, or OSX you have lost probably a majority of your stuff.
You CAN use a recovery software, but chances are 800% of the stufff you find will be currupt, and or in accessible since everything is fragmented all over your HD, and chances are bits and pieces have been overwritten.
Data recovery only applies if your HD dies, and you dont copy or put anything on it.. software, or even hardware can be used to recover files on broken HD's