Where did you store your files?

They should still be there unless you stored them in a program folder, said program folder having been removed during the upgrade.

Try a search (right-mouse the Start button, select EXPLORE, then right-mouse on the C: drive and select Search

Enter the first part of one of your files, ie for MyFile.Doc you can put MyF*.*
and then click the Search.

You should always keep a separate copy of your files, what will you do if your C: breaks and is replaced with a new one?