Resource types

Hello, I've been asked to solve an issue with the resources from main menu. The thing is that suddenly the main menu only shows the resource's title, but not the icon. When I click on the links I get the page with the title, and a message that says that no files have been added to the course yet, but they were there yesterday. I tried searching in the database, in the resources table, I find that the the resources not shown when I click on the main menu's links have something in common: - They are files. - The name of file stored in the resource cell has no extension (.doc, .pdf, .whatever). Why does that happen? How can I fix that? should I add the files extensions to the resources in the table? How can I prevent this from happening again? Next step, I'm going to look in the directories via FTP and make sure that the files referenced haven't been deleted, but I don't have FTP access from my location (proxy issues).