Do you know what’s the hardware version? Is it OS 2.x? If it has a USB port, the first thing you can do is to remove the 24VAC power, but instead plug in a USB cable connected to a USB power source to see if the controller powers up and displays anything. If so, it’s likely 24VAC->5V conversion has a problem, and there is a work-around (basically using USB to power the controller) to continue using it.