Have you tried going into ccc and see if you can get it to work.
Tried clicking lots of things. Couldn't get it to work. Both monitors are detected but somehow whichever monitor using the miniDP says no signal or cable not connected.
I used this converter in particular http://www.ebay.co.uk/itm/290826205217?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1497.l2649]
and then connected using the normal HDMI cable to the monitor. Could that be the problem?