23'' Cinema HD display doesn't turn on | LED shows nothing

Yes, I know this question was asked quite often already but I promise my setup is a bit different and in such a way that I as a non-Apple user am unsure what could cause what.

This week I got an A1082 for free since it was supposed to not work anymore. The giver told me that the display suddenly stopped working. The monitor is modified a little bit: Apparently the original power supply stopped working at some point and thats why he replaced the connector with a DC connector to use with one of the regular power supplies. And according to him that worked out for some time until said display stopped working.

Now I have the monitor standing here together with a 24V 6A power supply and a Windows pc with a gtx 1070Ti (including DVI). When I connect the monitor to the power and to the PC the monitor does show nothing - no backlight, no LED. The PC recognizes the monitor under “Cinema HD” and knows the resolution (1920x1200).
Connecting the USB cable to my PC seems to do nothing - I can neither use the USB plugs of the monitor, nor is anything else shown.

For me it seems like the monitor may not work anymore, but maybe its just a special case that I didnt stumble over yet. Maybe it just doesnt work with windows like it does with a mac (I could use my girlfriends one as soon as I have a thunderbolt to DVI adapter), maybe there might be an easy hardware fix, maybe it just doesnt work without a magsafe power supply (and the giver lied).

I hope someone knows some more about this topic. It would be a shame if I would have to throw this monitor away.

So I opened the monitor up to check if there is some obvious damages. But nothing that I could detect on the go. Am I right to believe, that the power in should be on the top the black connector right next to the flat orange capatior? Because I couldnt measure any volt there. I guess the cable could be broken (power supply is new and has ~24 volt out). Is there anything else I can check with a multimeter?