Does this list include new leads? If so, be sure to check the options you select during your upload. For instance the list import mode "Normal" will include new leads, but "Skip New Leads.." will not upload any new names.
Double check your excel list as well to make sure all formatting is correct for list uploads.
Great support article to make sure all is well: https://community.marketo.com/MarketoArticle?id=kA050000000KzWVCA0