If I take snap in low light in DSLR? - 1

If I open flash image'll be displayed as soon as I take a snap in low light.
My DSLR Nikon D5100 indicate to open flash. If I neglect and take a snap in low light, it takes 7sec to 10sec to display image on LCD! What is the problem in this case?

There's no problem. If you won't provide the additional light, the camera has to leave the shutter open the extra time to compensate.

The problem is that you have no knowledge whatsoever about photography. There's a few ways to get enough light on a photograph.
1.leave shutter open long enough
2.bring it yourself, i.e. Flash

Shoot in P mode. The camera is still in auto but you can change things. Look in your camera book how to do this. Change your iso settings higher. Remember that the higher your iso the more noisy your photo's become.

It's not just taking 7-10 seconds to display the picture, it's taking those 7-10 seconds for the shutter to open and close. When there isn't enough light, the shutter has to stay open longer to allow more light to the sensor.

You either need to:

A. Take the picture with a slow shutter speed and a tripod
B. Use the flash (or provide another source of light), or
C. Shoot at a high ISO.

I don't know how dark the environment is, or how high your ISO setting will go, but increase it gradually until the image is how you want it. The higher the ISO, the grainier (called 'noise') the image. Some photographers may be aiming for a style that works with noise occasionally, but in general, it's looked upon as low quality and the image will suffer.

I think it'd benefit you to do some reading. You don't need expensive classes or a fancy degree to do photography, but you do need knowledge. You can't get that from simply asking questions on Y! A.

The most basic fundamentals of photography include aperture, ISO, white balance, shutter speed, and composition. Start there - it's enough to keep you busy for a while.