It needs to be remembered that the natural, open 'folk' voice is considered ugly by many conventional (particularly classically trained) exponents and teachers.
If anybody tells you you are incapable of singing, get a second opinion - preferably from somebody familiar with the genre that interests you.   
In thirty odd years of work with singers I never met anybody who "couldn't sing" - plenty who were not used to it, and hundreds who had been told they would never be able to, but none who couldn't be developed with a little work.
Group work on individual singers really worked wonders with many new singers.
Jim Carroll