I thank you all for all your suggestion. Yes, turning it on in less than 24 hours was probably not the smartest move. We're experiencing 35 degrees in Norway these days (insane!), and I left it out in the sun a whole day and it seemed to be completely dry.
I decided to give this board one more chance, desoldering everything and doing it over. And cleaned the board with a tiny bit of isopropyl alcohol and a tooth brush.
All of a sudden, it works now. So there might have been some water shorting it out, I have no idea really. I don't really trust this is going to work forever, but I'm happy it finally works! I didn't have much confidence in my soldering skills so actually achieving something feels really good. So I went ahead and replaced the clock capacitor and thermal paste, and removed pin 6 from the lpc as this kept the Aladdin's red LED on all the time, even when the system is turned off.
Every once in a while I get a disc read error though (with both original and burned games), not sure what causes this. Maybe a bad dvd drive?