I am having a small issue in my viewsonic led monitor VX2458-MHD that nothing appears when I give input to the HDMI port.I read user guide of this model here https://viewsonic.com/me/products/lcd/VX2458-MHD.php, but nothing great found. I also tried VGA and DVI ports, still, the problem is there. What could be the reason? I am confused. If anyone here tells me why this is happening and how do I solve it, I will be thankful.