I have created a list with 20 columns and I have this issue: when I click to add a new item the newform.aspx page that open is empty/blank (no control shown at all)!
I never had this problem before. Any ideas what could be causing this?
The forms will be rendered based on the contenttype. So your columns have to be added in this contenttype. Simply write a contenttype for your table. In the List you set EnableContentTypes="TRUE" and add
Now your forms should work correctly.