Hi!
As you said the fiber LEDs are not lit, that means the ports are not 'up' so the stacking has not been done.
Log into your switches and then run the command 'Show int interface name' to know the status of the fiber ports.
Also check the connectivity of the stacking cables with the ports in the switch. Maybe you can take them out and then connect them again.
HTH, please rate the post if it does.
