What you've probably done is not lost your pictures, but incorrectly set the wrong program to use for them.
Can you still see the files themselves?
If so, hold down the shift key, and at the same time, right click on one of the picture files. You should get a menu, on which it says "Open with ..."
Click th open wth, then you will get a list of programs you could use to open the file. You need to choose the program you used to use for this (forget about the icons, just concentrate on the program names).
If you can't remember, try selecting Internet Explorer, or Phot Editor, or similar. If you have to try a few to get back to the correct one, don't worry.
When you make the selection you should see a small box marked "Always open with this program" (or similar) - put a tick in it, and whatever you choose will be used subsequently also.