If you try to save a document, does it go to the correct "My Documents" folder, or did you perhaps change the location by saving to another folder by mistake? Try saving a document and see.
Also, when you go to open a file, look at the bottom and you'll see an area where you can type in a filename (useful if you have a LONG list of files), and the area directly under has a listing of file extensions. if you are looking for, let's say an Excel
file that was saved as Example.xlsx and the drop down menu is looking for a file ending in .xls, the only files that you will see are the .xlsx files, not the other .xls, xlsb, xlsm (etc.) files. You can switch to show all file types as well in the drop down
menu.
I don't know if this was helpful at all, but it is a common mistake for people that do not use MS Office products frequently.