Info from site at your link.
Ok,
So you have to reset the box. Sorry, no reset/panic button.
You need the image of your 60 box. Just download it from:
https://support.fortinet.com/
After you have to
Power off the FGT unit and use the following :
* Terminal client (windows hyperterminal, linux minicom...)
o Speed 9600 8 bits, no parity, 1 stop for all FGT
* Null modem serial cable (provided with the Fortigate)
* Provide a fixed IP address to your PC eg: 192.168.1.168
* tftp server running on a PC
# Connect your PC LAN interface using an eth cross cable to :
* "Interface Internal"
# Power on the Fortigate Unit
# Press any key at when "Press Any Key To Download Boot Image...." message will be displayed
# Enter the IP addresses
* Enter tftp server address [192.168.1.168]: 192.168.1.168
* Enter local address [192.168.1.188]: 192.168.1.188
* Enter File Name [image.out]: image name.out
# Traffic should be displayed the TFTP server ( ensure image is located in the appropriate folder)
https://support.fortinet.com/
Sounds complicated. For me anyway.