Start > Run > hypertrm. Configure Com1 or Com2 connection, click Load Defaults, click OK. Connect with the console cable, power-cycle the device, then do the following.

Fortigate password reset:
login: maintainer
Before the password, type bcpb then paste the serial number.
Password: ********************
Welcome !
# config system admin
(admin) # edit admin
(admin) # set password 123456
(admin) # end
# exit