You might have FileVault turned on. Macintosh hard drive is locked and invisible in recovery mode when FileVault is turned on until you turn it off or unlock the disk by supplying the FV password. When you get to recovery mode select disk utility > Select the hard drive name from the list on the left and go to File menu > Choose Unlock or Turn FileVault off. You will need the password for FV and then go back to terminal. Try resetpassword command.