You have most likely blown the fuse on the back panel of the unit. Check near the AC receptacle for a screw type fuse holder.
If using with 220-240V, then a T500mA 250V fuse will be needed. If using with 100-120V, then a T1A 250V fuse will be used.
Make sure to set the red switch back to the appropriate voltage for your country before plugging/powering the speakers back on.
If this does not solve your issue, then I would suggest filing a support ticket at http://www.presonus.com/support/Contact-Technical-Support
or reaching out to the nearest distributor in your area for repair.