Nikon D40 not turning on?

A friend was using my Nikon D40 when it made a loud popping sound when trying to take a picture. The camera then shut itself off, and we have not been able to get it back on since. My warranty has expired, so I'm trying to find any ideas of what might be wrong with my camera, or if anyone has had a similar problem.

Loud popping sounds are not good. My best suggestion is to send it in to Nikon to be repaired.
http://www.nikonusa.com/...epair.page