Reinstalling Lightroom 5 - key will not get accepted
So I've had my MacBook Pro laptop crash hard on my and I've had to basically restart reinstalling everything from scratch, including Lightroom which I was able to copy over from one of my backups. Upon first opening Lightroom I was prompted to enter the key I har originally received and it was accepted, however, then I got a pop up telling me to update to the newest version, which I did, only to have that program asking for the key poping up again. However, this time it wouldn't accept my key, instead telling my key is not valid. I've tried all the steps of reisntalling lightroom, deleting certain files etc. to no avail.
The exact error message is: The entered serial key is invalid. Please try again. If you keep receving this error contact support. (translated from german)
Frankly I'm out of ideas and I'm getting more and more annoyed. Please help.
MacBookPro OSX Mojave
Lightroom 5 (.7.1) (Swiss (German))
