In my game, there is a question mark in a circle for selecting a crate to set alight. I cannot find a corresponding key, other than tab, but that doesn't work. Any ides?

I have not played the game in some time but if i remember correctly to burn creates you need to equip a torch, light it from another torch or fire and then go to the object you want to burn and either press the attack button or the button you use to pull levers.