does it say that the mode is not supported? if so do this.
you will need a second monitor (most likely the tv in the living room)
HDMI Cable
iPad or an iPhone (optional)
iTunes Account
iTunes credit to spend (£20 or more)
Step 1:
plug your Mac into the second monitor with the hd cable, plug in the stuff you need (etc..)
Step 2:
open the Mac App Store and search " Air Display "
The iPad way is cheaper. on the iPad you just search " Display Pad "
then, you google display pad or on the iPad, follow on -screen instrctions.
Step 3:
bring in the monitor, then put the hd cable into the monitor after you have connected your ipad/ iPod/iPhone etc..
to your mac.
Step 4:
on the device, go into the preferences, then screen settings, then set it to 720p, if that doesnt work, try cycling through all of the resolutions. if that doesent work, then try using the idevice as an extended display. then repeat.