Corolla 2006 stereo blank after installing AUX?

Hi all,

So I just installed an AUX cable in my hatchback Corolla 2006 with a OEM
Panasonic W58814. Bought this one:
https://www.ebay.com/itm/262224036269
Disconnected battery and installation seemed physically ok with the cable
fitting ok in the empty cd changer port, but now the stereo isn't coming an at
all. Display is blank, no response when pressing buttons. The small light on the
little AUX box isn't lit up either.

However, what I can hear is a buzzing sound from the stereo every second or
so after turning the car on. It sound just like the (empty) cd tray is checking for
a disc or something, so the stereo seems to be getting power at least.

I haven't tried disconnecting the AUX cable yet.

I'd greatly appreciate your thoughts on this one!