Since it works with standard vga cable just fine, only course of action might be to use the nvidia control panel's brightness setting if you want to keep using hdmi.
On other hand, vga would also work just fine since it's limited only with high refresh rates and high resolutions neither of which are supported on the monitor so unless there is some other reason to use HDMI specifically (headphone jack on monitor?) there is no real reason to favor HDMI over VGA.