Is it discrimination if I was told that I didn't get a position because I have conrows in my hair?

You may have a valid employment discrimination case.  It is illegal for employers to consider race when making a decision whether or not to hire or fire employees.  It is fair to say that having cornrows in your hair was racially charged to say the least. 

You should contact a local employment attorney or legal aid clinic and have them review the facts more in depth.  If you have any documentation from the prospective employer--keep it.  You should write everything down that you remember them saying to preserve that information.

Best of luck.