Solved! 
I used the router's guest account before, and when I had the idea to use the main account, I got Error Code 003-1101.
Things I did (with the help of the router/internet provider help desk).
- Power Cycling the router/modem combination (turning it off and then on again).
- Changing the Radio Channel from automatic to a free channel (one that wasn't occupied by neighbours at that moment, in my case channel 4).
- Using a different network key (I was using the normal self-chosen password at first, but apparently I needed the full digit one found at my router's settings under 'security').
I'm just putting it here for other's troubleshooting sake.