Lcd display not working on nikon d40. When we turn on the camera, and take off the lens cap, the lcd display is black. we can use the viewfinder to take a photo. We can view the image after taking the photo, but can not see the image prior to taking the picture.

Does the menu show when you press the MENU button? Can you see your pictures when you press the Playback button (right-pointing triangle)? If so, then there's nothing to fix.
The D40 works as SLRs have worked for half a century. There's a viewfinder which allows you to frame and compose your picture. The LCD monitor is for menus, camera settings, and picture review. LiveView, which allows you to use the monitor for shooting, is a recent development, which Nikon introduced into their cameras with the D3 and D300, both introduced years after the D40.

There's nothing wrong with your camera. The D40 works as SLRs have worked for half a century, using a mirror to project the image through the viewfinder. The live view feature is a relatively recent development among dSLRs, previously available only on point&shoot cameras.

The D40 does not have the LiveView capability. It works as SLRs have worked for half a century, showing the image through the lens via a viewfinder. This has changed in the last two or three years, now the only current dSLR in Nikon's lineup without LiveView is the D3000.

Sorry that wasn't the answer you wanted to see, but I can't tell you how to do something the camera simply cannot do.

I don't believe there is. Nikon call it Live View in other models, but its not mentioned in the D40 user manual.....

here's the full manual, if you'd like it.
http://safemanuals.com/user-guide-instructions-owner-manual/NIKON/D40-_E

while using slr cameras u always see in the viewfinder bcuz slr is a single lence refleime u can see the picture after shoot by clicking on play back option this is a feature of an slr camera

If you are talking about viewing the shot you just took, press the "info" button on the top of the camera (next to the shutter button), that will turn the LCD on and off.

According to Nikon, that was not possible. The D40 doesn't have 'Liveview' like the smaller compact cameras. You would always have to use the viewfinder for taking pictures. Even in the TV ads, everyone used the viewfinder as they took turns using the camera.

Here is a link to Nikon's web site: NikonUSA

Try pressing the "info" button on the top of the camera next to the shutter button. This turns the LCD off and on to save battery life.

The camera has a mirror lock up feature for cleaning the CCD sensor. You may have engaged it. Check your manual about this function

Since the camera is an SLR, (single lens reflex), the CCD image sensor is behind the shutter until you take a picture. Sorry, but you cannot use the LCD to take pictures.