Welcome to ask.fedora. Please understand that all new accounts are moderated and your posts won't show up until approved; asking the same question twice won't get it posted any faster.
Now, to answer your question, useradd expects you to give the encrypted password. I'm not sure why this is messing up the root password, but it's not going to get the new user's password right. Try creating a new user, but not giving it a password. Then, use this to change the password:
passwd $NEWUSER
and follow the prompts. That will get the new user's original password set, and shouldn't change the root password. And, for asking a good question, I'm going to give you a little karma so that you can vote good answers up if you feel it appropriate. Good luck, and I hope this helps.