Canon 580EX II don't to fire with Cactus v2s wireless reciever by GI. Why? Help me.
set the flash to manual.
the battery for the receiver is covered in plastic. make sure you've removed that before installing it inside the receiver.
make sure the radio frequency setting matches between trigger and receiver. check that both trigger and receiver have the same dip switch setting (you can find that underneath the trigger and inside the receiver)
finally, there's also a change that your batteries are dead. note that you need to open the trigger with a screwdriver and take out the its battery.