Thanks Bob, I did change it to WPA some time ago...
so, that isn't the problem.
However, this afternoon when I felt really desperate I found the CD that came with the router and ran it to set it up again. At first it didn't work, then I ran the troubleshooting part and after a few things it began to work again. I'm so happy right now you wouldn't believe it. I've spent all day on this stupid thing.
So, thanks for your help, and if I get stuck again I'll be back.