I want to import a file to a table, but when I go through all the steps nothing imports. Help!?

I'm trying to import a file (.txt) to update a table. I'm a group moderator. (SDMC-List). When I go through the steps (Edit Table, Import, select file, Open), nothing happens. No info imports. What file format should I be using? Also, I cannot DELETE the previous attempts to do this update. Trash can not working.