Laptop keyboard after installation is no longer correct - how can I get it back?

My old DELL laptop had problems with the keyboard, some keys did not react or only rarely. Only certain letters were affected. So I ordered an original DELL keyboard for this model, removed the old one and installed the new one. The laptop started up and now I can't do anything with the keyboard.

The return key now writes a "j", the key "A" does nothing, even the caps lock key does not work, other letters are hopelessly reversed, a "B" becomes a comma.

I realize that something went wrong, but what? The keyboard cable is inserted with the side up (yes, UP is also on it) correctly. Keyboard layout is German.

How do I get this totally spun keyboard layout right again.

It's been dealt with. Have the old keyboard installed again, now it fits again. I was probably sent a wrong keyboard.

These keyboards are often connected to the laptop by means of these flat foil contact bands.

Maybe the cable has slipped or it may even be damaged.

So: reopen and control.