oh you already tried ok, once check whether both the repositories exists or not
and also remove those repositories and intall them again and link provided for epel repository in the article is not working so try another link to configure epel repository.
also check those repositories are enabled or not by editing /etc/yum.repo.d/epel.repo and /etc/yum.repo.d/nux.repo
enabled=1 (if enabled =0 then change to 1)
for reinstalling repositories just remove the existing repos by using rpm
#rpm -ev epel-release***
#rpm -ev nux-desk****