It happens all the times with the icons, windows gets mixed up on what icon it is suppose to show and you get a white box instead
Try this one, go to the control panel and then default programs. When it opens click on "Associate a file type"
When it opens you will have a very large list, instead of hunting down all the ones you need, lets just try a few and see if it works first.
So depending what file type is the word docs on your desktop you can do set .doc and .docx and for excel .xls and .xlsx and lets see if that does the trick.
Another trick that I have done on customers machines to get the icon to reset as well, go to one of the files, right click on it and go to "open with..." when you mouse over it, it will give you a list, click on default program at the bottom of that list.
When that list opens you can choose the default program for it and then put a check ont he box at the bottom to make it the default and hit ok. That will normally get explorer to write the icons again.
Shane