Seems like I had a trial license that was overrunning my true license.
To solve it, I did the following:
Set computer to airplane mode.
Open GameMaker. Airplane mode made it unable to verify my 30 days trial license was expired.
Log in, offline mode. Game project opened.
With GameMaker active, activate internet and open GameMaker.
It logged me off, and relogging in made my true license overrun the trial license.
Reinstalling did not make it work, abusing in a way I'm pretty sure that would allow piracy did. Good job.
Please fix. I have the license, I shouldn't be stopped to use because I was given a 30 day trial that expired.
Also, that 30 day trial expired a month ago, there is no reason for it to not have happened yesterday. It happened conveniently when I had to show the project to another person.