Which model? That's a crucial bit of information.
Lots of things go on without a license. But a Fortigate without a license is still a powerful policy based UTM. You can also enable AV/IPS and other features but it won't update the sigs, but the existing sigs will offer some nice extra protection even without updates. I can turn an unlicensed Fortigate into a fortress, so can you if you know your way around the GUI and CLI.
Also a bit of new information kids - ALL Fortigate's now come with the enterprise bundle. That's Sandbox+Mobile Malware Detection and some other goodies as no extra charge. Before that stuff could add up. Now it's part of any basic bundle. No license? FortiSandbox still works, but only to about 100 files a day. If you want more than 100 you need to pony up for a Sandbox license (about $80 a year ish)
If you don't have a valid license you can't find the firmware upgrade path and download the firmware to bring it up to date unless you know someone with access to the Fortinet FTP server. <wink> Then you can PM them and get the path. Provide the Model, existing firmware version to said person.