I want to use my iMac display as a second monitor for my laptop. I have a 2013 27" iMac for personal use. I have a 2011 HP Elitebook 8440p for work. This has a DisplayPort (not a mini DisplayPort). It also has a VGA port. I bought a DisplayPort -to-min DisplayPort/thunderbolt cable, plugged them into each machine, but got no results. Any idea why this didn't work? Thanks all.