Is it just a specific version of Archicad that is not starting. or is it all versions.
Is it trying to start in demo mode even though you have the USB key plugged in or is it just not starting at all?
If it will only run in demo mode with the key plugged in, have you used the License Manager to check the key?
If the key is not being recognised then I would suspect a problem with your USB port (try another one if you can), or maybe a problem with the key itself (can you try it on another machine or do you have the opportunity to try another key?).
Or maybe re-install the latest Codemeter drivers.
Easiest way to do this is to download the latest version of License Manager and re-install it.
One of the forum moderators.
Versions 6.5 to 25
Dell XPS- i7-6700 @ 3.4Ghz, 16GB ram, GeForce GTX 960 (2GB), Windows 10
Dell Precision 3510 - i7 6820HQ @ 2.70GHz, 16GB RAM, AMD FirePro W5130M, Windows 10