As you might be able to tell by similar posts, there are some issues with the latest 7.4M2 drivers when used with Optimus (laptop) platforms. (blank screens, DirectX issues)
You can try the 7.4M0 drivers to see if they resolve the problem until DisplayLink releases a new version of the drivers.
Link here:
http://displaylink.com/support/sla.php?fileid=98