How can I open a picture file in PS Elements after installing service pack 2?

Since I installed service pack 2 on my HP computer a week or two ago, the Photoshop "Open" tab no longer appears at the top of my Pictures screen, but rather a "Preview" tab, and I haven't been able to open a picture in Photoshop.  Instead, when I double click on a picture, it opens in Windows Picture Gallery.  Not long after I installed service pack 2, I also changed my default browser from Internet Explorer to Mozilla Firefox, so I don't know if that has anything to do with it.  Thanks...