Be sure to be using the latest BIOS posted here:
Then install the latest video driver here:
Intel® Iris™ and HD graphics Driver for Windows 7* and Windows 8* 64
If the issue persists, test using only the display connected to the HDMI port. Additionally, you may need to test a direct connection between the HDMI port and another display as the issue may be caused by the adapter/converter that you are using.