Gateway or Toshiba?
Sorry, it's not clear what you have.
Have you tried a System Restore to a date back to when it worked? If you cannot access System Restore in normal mode, try that in Safe Mode.
If this is XP and System Restore fails, try the .exe fix in the list at http://www.dougknox.com/xp/file_assoc.htm
For Vista, try this utility; http://www.thewindowsclub.com/file-association-fixer-for-windows-7-vista-released
My son uses my computer and left it on me with the following error popping up each time i try to open a file. "This file does not have a program associated with it for performing this action. create an association in the set association control panel"
System is Gateway Toshba, XP-VISTA, 2gig mb, 120HD.
What should be my next move.