So, my cinema display is sending short long short...

Okay, so my cinema display is sending short long short. That means I have a pwer supply probem, apparently. But I have two screens and so can swap over the power supplies; the one giving the error message continues to err, so the fault is not with the power supply but with the screen itself, right?

The screens having been working perfectly for years (five?). All I did was carry them between buildings. A static charge is a possible occurrence here in a dry part of China. The screen has working ports - the keyboard I am using is driven by the faulty screen (the screen procaliming a fault, really).

What am I missing? I'm out of ideas - and, being China, help is a long way off.