I have two laptops and when I either install elementary OS Freya or run it off a USB. Every time I connect a monitor to the laptop the system responds very sluggishly. For eg: When I click on any of the dock icons it takes a good 12 seconds to respond. This is the case with all icons in fact after I connect the external monitor.
I have connected two different monitors to two different laptops and experiencing the same issue. I have also re-downloaded elementary OS Freya and done a update and an upgrade with no resolution yet.
Any advice would be appreciated.