MPC KEY 37: Dreaded "INVALID SERIAL NUMBER" problem!

Hi. I am new to MPCs and after trying MPC with a second hand STUDIO controller I decided to try that new MPC KEY 37.
I got a good one on EBay from a guy who sells left over stuff. The machine looks like new and as if it was never used. The display looks pristine like the rest of the keys, buttons etc.
After booting it and connecting it to my wifi, I loged into my inMusic account and registered the serial number from the bottom of my KEY 37. Everything looked legit. It started downloading and installing MPC frmware 2.15.0 and rebooted. After connecting it with my wifi again and downloading a plugin, I found out that no buttons are working and no sound is comming out of the any output. The MIDI ports also don't accept any data from external keyboards. Only the screen and all it's menus work, but none of the physical buttons and the keybed!

How do I get this thing working again? How do I register the valid serial number Akai's website accepted with my machine? Some people on this forum posted about this problem with their MPC ONE hardware and solved it? How?

Please help!

Have you logged a call with Akai?

Was it working before you tried the new Firmware?

@NEODYMIUM

Yep. I opened a ticket with AKAI support. I still hope they can unbrick my hardware.
I am not sure, but maybe too many people registered the same hardware for some reason? Which sounds implausible since the KEY 37 looks like it has never been used and isn't that long on the market.
Many forum posts seem to suggest to go back to firmware 2.10, but that dose not exist for KEY 37. Earliest version is 2.13
Looks like I have to send it in to an AKAI service center somewhere here in Germany or Europe.

Cool, at least you have a valid serial code with Akai, so they should be on it. I can't offer any suggestions, just seen you have done searches for similar problems. Give it a little time, and I'm sure you'll get some of the gurus on hear being able to offer some help.

There used to be a special diagnostic mode for reserializing the unit, im not sure if its still there. the "testapp" stuff in the rom. i also forget the hot keys to get into diagnostic mode. iirc somewhere in there you can fix it though.