It can be an OS problem, MS Office Suit problem or File Corruption issue.
What about the other MS Office programs? Are they opening? Are you getting any error while you try to open these files??
Make a copy of your Word/Excel/PowerPoint file and try to open it in some other computer. If it works that means the file is file. If it doesn't then its a file corruption issue. Have a look at this resource article for help and safe recovery.