Did you try a different monitor and another hdmi cable,
or tested the cable and monitor with another device?
I had an issue with a computer at work that aften an update refused to output any hdmi signal to the hp monitor, it worked via vga so I figured it was a driver issue. Reinstalled various driver versions until I found that it was the monitor hdmi input that was the problem. Swapped to an identical monitor and hdmi was ok.
