Monitor not working at all?

I bought a used Thunderbolt Display. It was sent to me and I wasn't able to check it upon purchase. When it finally came, I saw the housing was in very good condition, no scratches, no bumps. Cables are fine and clean. When monitor is plugged in to a power supply my MacBook Pro can be powered too (the small led correctly indicates charging).

However:

- USB ports dont charge any connected device (like iPhone)

- when connected to laptop, the monitor is neither listed in the monitor list, nor in the thunderbolt section (computer states: no thunderbolt devices connected)

- the same when monitor is connected via a separate thunderbolt cable (not the one going out of the back housing)

What can be wrong? Is there a chance to fix it by myself or service is required?