The simple solution to this is to right-click one of the files you are having a problem with and then select Open With to choose the program. When the next window come up select Microsoft Word and check the box at the bottom to 'always use this program to open files of this type.' That will set Word as the default program to be used to open the files when you double-click them. You may have to repeat this for files of different file types. (.rtf, .txt, etc)
Hope this helps,
My computer consistently changes Word docs to Wordpad, even though they are created in Word. It does this when I save (unless I save as an rtf file) and when it opens a Word file sent through email. How can I correct this?