ASUS GL552VW HDMI issue

Hi,

I have an ASUS GL552VW with i7-6700HQ CPU and Nvidia GTX 960M.

I have a problem with my HDMI. I have an external LG UltraWide monitor and when I connect my laptop the external monitor starts flickering and disconnecting.
I have sent it to a repair shop and they told me when they connect it to a monitor, there is no problem, so the port is not faulty. They suggest is my cable, but I have tried 2 or 3 cables, one of them i bought new.
Has anyone had this problem and do you have any advice or solution? Maybe it is the drivers?