Character won't move

I played about 1.5 hours now. My character advanced a few levels and now, it won't move anymore when I click the ground, no matter where I click. I tried two mice, that work perfectly well with any other programme. I always played with the mouse, never used a game pad. Even restarting the game and also rebooting the PC didn't solve the issue. The character keeps standing in one and the same spot.