[TGB!]

The reason I suggested it was underexposed was from looking at the histogram. A lot of people will say "oh thats over/underexposed" and be going off person preference instead of what the numbers say. In the histogram of the original theres alot of information in the darks, but theres nothing past maybe 180 (on a grey scale of 0-255), which means you lost information in the light section of the photograph.

As for the noise (the choppiness you see) - you can see that evidenced in the original photograph as well; I'm guessing that the auto-iso setting chose something a little high, maybe 400 or 800 - not too familiar on how well the D40 handles noise at higher isos, but bringing out the highlights in a photograph will do that.