I just upgraded to Windows 10 from 7. My external Acer monitor (G276HL) was working fine with my Acer laptop(Aspire 7745G) with Windows 7. With Windows 10 the external monitor does not get a signal via the HDMI port. I switched to a VGA hookup and this
allowed me to use my external monitor. Why does the HDMI hookup no longer work?
This might have caused due to Network Adapter driver compatibility issues. I suggest you to try installing the Graphics card drivers in compatibility mode and check if it works for you. This is to check if this is caused due to any driver compatibility issues.
First of all, download the Graphics card driver from Acer website and then refer to the following Microsoft Help article top install the driver in compatibility mode. The steps for Windows 8.1 applies to Windows 10 as well.