My WLAN connection stopped working and I don't know how to handle the problem. I would appreciate any help.

Router, authentification etc can't be the issue, because I am online with my smartphone and netbook.
I don't expect any driver problems either. It was working just fine about two hours ago and I didn't change anything on the system.
It tries to connect, doesn't manage, asks me password, I enter it (again), and then back to the start.

I applied the pathetic treatments like reboot and waiting it to get well by itself makes me lose my self-respect. I don't know what the problem can be. How can I diagnose it?

Thanks in advance!