I have bought a HDMI to Displayport cable on the assumption that it would just work, but it doesn't. As this is my first foray in to the displayport territory I am stumped. I am using a Dell U2412M ...
Not all HDMI ports are created equal, though that is a common misconception for folks who may not be a display tech ...
There is a possibility that an outdated and corrupted display adapter driver is causing the problem. You can download the display adapter driver from its manufacturer ...