Without Superuser you lose root. Without root, you can't install Busybox.
BusyBox should download just fine, rooted or not.
If you need further help, or want to explain,
join the Android Central community, and you can post in this thread instead of starting a new one every time.
(About the only way of totally removing root, if that's what's causing a problem, is to reflash the phone's ROM.)