problem with Ms Word 2003

Hi!!!!

I have ms office 2003 in my desktop
the issue is that when i open a word file a dialog box with heading File conversion – File name appears with option like Windows Default, MS-Dos, Other encoding while the content does not show up!

what this could be? a virus?
How can I recover my files coz most of them are affect and are important?
what could be the cause of it?
How to avoid it to happen next tme?

Thanks.