The camera won't register an image to take a picture of.

See this FixYa link.

Try the procedures in this tip.

seems like a bad inverter that needs changing

Since the D40X is an SLR, (single lens reflex), it is not possible to use the LCD monitor to frame your pictures before they are taken.

To view what your images look like after you have taken them, you need to use the 'monitor/play' button marked with a rectangular box

An adapter tube has to flare out at the end or it will cut the corners off at the wide angle setting. Telephoto should be ok though.

The LCD viewer is made up of the LCD screen, and the backlight. Your backlight is burnt out, or the circuit board isn't sending power to it. Backlights can be replaced separately.

The e fall dames the camera -evidently There is not user repair possible Contact Nikon for a repair quote.

If you turn on the back LCD, the electronic viewfinder will remain on while in a shooting mode. There is no setting on the camera to use only the back LCD monitor while shooting. If you playback images in the Play mode, only the LCD monitor will turn on. However, if you press the Monitor button while in the Play mode, than the back LCD monitor will turn off. The image will display only in the viewfinder LCD.

If you turn on the back LCD, the electronic viewfinder will remain on while in a shooting mode. There is no setting on the camera to use only the back LCD monitor while shooting. If you playback images in the Play mode, only the LCD monitor will turn on. However, if you press the Monitor button while in the Play mode, than the back LCD monitor will turn off. The image will display only in the viewfinder LCD.

If you turn on the back LCD, the electronic viewfinder will remain on while in a shooting mode. There is no setting on the camera to use only the back LCD monitor while shooting. If you playback images in the Play mode, only the LCD monitor will turn on. However, if you press the Monitor button while in the Play mode, than the back LCD monitor will turn off. The image will display only in the viewfinder LCD.