Magellan GPS

If you format the hard disk, that mean you formatted the part being used as the "ROM" (Read-Only Memory). In other words, there is nothing you can do to fix that. Unless you're referring to an SD/MMC card, then you might be able to restore the data using some recovery software, I prefer going to http://www.piriform.com/recuva and downloading Recuva.
Although this is recovery software, you might not be able to recover all the data if data has been added to the drive.

does anyone know how i can restore my hardrive on the magellan i formatted it by mistake