What's wrong with my computer?

Most likely when you restored, it returned to a date prior to the installation of a program that was used to open the file you are trying to open. For example, it is a wma file and the restore point was before you instaleld windows media player (which plays wma files). What you need to do is find out what program it is the you are missing and redownload/reinstall it. Do a google search for the file extension of the file you are attempting to open and that should give you a good clue what the program you had that is used to open it.