Over exposure display, Nikon D40?

How do I get the feature turned back on that flashes the overexposed portions of the photo on the display after taking the picture? Mine has stopped and I use that quite a bit with manual lenses.

That is to tell you to stop your lens down when using your flash under those conditions.

If you look in your user manual, it will tell you how to turn off the highlight warning screen

When you are looking at an image on the LCD, just tap the multi-function switch (the round toggle thing) up or down a couple of times and it will cycle through the various display modes, including the "highlight" mode that you are looking for.