Hi,
I am not sure that the FG-200B has a log disk or only some flash.
Check the cli settings:
config log disk setting
set status enable
set storage <disk, memory, FLASH> --- usually these are the options !!! changing the storage may require to reboot the device !!!
or
config log memory setting
set status enable
The most important is to check where the logs are stored and set the gui settings to read these logs:
config log setting
set gui-location <memory, disk, fortianalyzer...>
If I were you I try this:
config log setting
get
--- check the gui-settings if it is memory, disk etc...
than
config log disk setting
get
config log memory setting
get
--- check the " status" enable/disable at these two options. If you have somewhere enabled than set the gui-location to that.
Optionally you can set to log to disk, flash etc with the commands above. Be aware of the possobility that the FortiGate will need to be restarted. It will warm you and ask you whether to continue and reboot or discard the settings and not reboot.