I've had that problem also before, you actually are typing but it doesn't echo back to your screen. I ended up with a strange user name because I hit a few letters then hit the enter key.
When I did it, it put my normal user name in the box but I couldn't read it, hit enter and see if you get past it. Not sure what would fix it, it only lasted one day for me. (I attribute it to my ISP doing funky things)