You can right-click on the document, go to "Open With..." and choose word/excel from the list. This will make sure either program is correctly set to be used with the corresponding documents. It should also go through and refresh the icons for all files of those types.
Otherwise, right-click the document, go to properties. I can't remember exactly which tab it's under, but there's an option to "Change Icon" you can use to change it back.