I can't upload my pictures to facebook, picnik, etc?

I have a Nikon D40 from my school, I uploaded the pictures to my computer but was unable to view them until I downloaded a Nikon software. Now I can view the pictures on my computer but it won't let me upload them to facebook or picnik. How can I fix this?

What format are they in? Jpeg? I suspect not since you had to install Nikon software to view pictures. Convert them to jpeg and you should be able to upload them.