Hello and welcome to Sythe.
We're probably going to need some more information.
Exactly which files are spoiled? Docs, images, music, videos??
Are they corrupt or are you simply having a file association issue. Perhaps reinstalling or repairing the application you use to open such files will repair the file association problem.
You mention "Excel" in your post title, are those the only files that exhibit the problem?
IF they are simply not displaying the contents properly you might have a look here SOLVED - Latest Windows 10 Update corrupts Ariel Narrow Font