macbook air 2013 connection to external ultra wide monitor

I'm trying to connect my MacBook air to a gigabyte G34WQC monitor. The HDMI connection works, however, the view is stretched. I'm trying to use the display port but the monitor is not registering the output. The computer itself recognises the external monitor (make and model show in the display option) but the monitor is showing as having 'no digital input signal'. Does anyone have any experience with this or advise on what could resolve the issue?