Need help! Unretrievable documents

Help! I am a full time online student and save all of my discussions, projects etc. in a seperate folder for each class. For some reason I recently tried to access these and it keeps giving me errors, either: "the office open XML file Access Class cannot be opened because there are problems with the contents" and when I click on details it says "the files are corrupt and cannot be opened". WhY? Before 2 days ago they were fine. When it offers to recover the contents and I click yes it says " ...cannot open because some parts are missing or invalid". I thought maybe my husband screwed up some stuff but he swears he didn't do anything abnormal. I need a solution or that is alot of work I have to redo! help, anyone!