Not doing the same things it used to do

I had to erase and reinstall everything on my macbook (done at mac store). Since then there are some operational issues, nothing serious but annoying.

I like to post pics to several sites and I seem to have issues doing that now. When I'm on the said website and it asks to upload file/choose file, iPhoto used to pop up and I just picked the photo I wanted to upload. Now, my Finder opens and when I select iPhoto in Finder, there is nothing there.

Any suggestions how to get iPhoto to come up as it initially did?

Thanks for any assistance.