Sounds like either the key has become corrupted (damaged) in some way, or the USB port is not working.
Try a different USB port.
If you have the License Manager Tool on another computer, you can try upgrading the key there.
I assume the key used to work with you previous version (24?).
Is that still the case - can you still run your previous version with that key?
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