Hi Tweed and welcome to the forums! So sorry for the trouble here–let’s figure this out together.
First off, will you please manually reinstall the plugin? We have a handy guide to help walk through the steps to do this. Your data will be completely fine, though it’s always a good idea to backup your files and database when making any update in WordPress.
Once you have the latest versions of both The Events Calendar and Events Calendar PRO installed (both are at 4.0.7), head over to Events > Settings, click on the Licenses tab and see if you are able to enter a license from there.
Cheers!
Geoff