Nikon D40 camera will not work!

SOURCE: nikon d40

Take the lens off and continue pressing the shutter untill it doesn't react anymore, you should then have a normal menu without the error message.Put your lens on and you're all sorted.Cheaper and less hassle than sending it to Nikon.
olly

SOURCE: Nikon D40 Memory Card Error

Hello. Make sure the write-protect switch on the SD card is in the UP (nearer to the contacts) position. Try the card in an SDHC capable reader on your computer first. Note that the SD card can only be inserted one way - make sure you're not putting it in upside-down! If the computer recognizes the presence of inserted card (whether it can read it or not), format it at FAT32. When finished, remove properly (icon in system tray) and insert into your D40 slot, WITH THE CAMERA OFF!! Turn on the D40, and if it now recognizes the SD card, FORMAT it again, in the camera. Good luck.

SOURCE: problems taking pictures with nikon d40

Chances are good that it's not your camera, but your lens. In a darker atmosphere, you need a fast lens, meaning you need a lens that has a wide aperture (1.4 to 2.8) I'm guessing you're using a lens thats' 3.5 or larger. (Yes, the larger apertures have the smaller numbers)

If your camera was spending all it's time moving in and out trying to focus, it's probably because there was not enough light for the camera to distinguish a focal point. Same thing happens when you shoot a solid blue sky. No focal point.

Help me understand by telling me what lens you're using and what settings you were using on the camera.