Thank you for joining the Intel communities.
I assume you have the Intel® HD Graphics 4000.
This information is straight from the Configuration 3-Displays FAQ page. For the Intel HD 4000 to actually support the three independent display configurations, the following criteria need to be met:
If two of the displays are DisplayPort* monitors
If one of the displays is an Intel® Wireless Display (Intel® WiDi)
If the built-in display is an Embedded DisplayPort1 (eDP) not a LVDS
The above information shows the three configurations needed to get the three displays. It is not recommendable to use video adapters or convertors.
Another good step is to confirm with the computer system manufacturer if your computer can run the 3 displays configuration because sometimes the system manufacturers set limitations on the units.