Take the wire from the speaker that is working and plug it into the one that is not working, do you get sound? If so it may be your cable.
If you don't get sound, then you first should check the fuse.
In the power connector on the back of the speaker, there is a pop out fuse holder, make sure the fuse is not blown, if it is replace it with the spare in the holder. If it blows again, then something may be wrong with the speaker. If you're in the USA, file a support request with us online at http://my.presonus.com
, if you're outside the USA, go back to the store where you bought it for warranty or out of warranty repair assistance.