(United States, MO)
My little kitten won't stand on his back legs and his neck can't stay up or straight. Also, he loves to run but he can't walk.
Without seeing your kitten and having more details, I can't begin to know what is going on medically. The fact that you say that he can't walk and he holds his head funny, but that he can run, makes me think of cerebellar hypoplasia. However, as I said before, I cannot know for certain.
If you haven't done so already, I would strongly advise you to bring your kitten to a veterinarian to be examined right away, as his cat illness symptoms could be serious.