I have a Nikon D3100 and surprisingly the dial mode does not work properly. I mean when I turn it, at some modes, it shows the selected mode correctly on the display, but not for all

On you camera's mode dial, you will see an emblem that looks like an encircled downward pointing lightning bolt. It should be located below the "Auto" symbol when the camera is in the auto mode. Turn the dial to that setting and your flash will be disabled.

What do you mean by flash mode?
Have you read the manual how to use the camera?
If nothing from there helps, try connecting it via USB and check if there is firmware update. If even that doesn't help, try acessing menu and doing hard reset from there.

If you have set the main dial to the green camera logo, with automatic in bad light, and the flash still does not pop up, you could start worrying. The mail mode dial is very easy to turn, even without knowing. It happens to me more often than I would like. My next camera must have a special button to lock this dial.
When you chaco the manual, you will see there are settings the flash won't pop up and even when it is up it won't flash, because that menu excludes the flash.

The lens is a manual focus lens. It doesn't matter which mode you have the camera in, you'll still have to focus it yourself.

Are your pictures properly exposed and are they sharp or are your pictures degraded? Is that 1/3-second you describe a delay between the time you push the shutter release and the time the picture is taken or somthing else? Check to make sure you're in the proper shutter release mode (slider switch to right of the mode dial). Also, your self-timer may be turned on. Your camera allows you to set a 2 or 10 second delay from the menus. If it is set to 2 seconds and turned on, it might seem like a 1/3-second delay. If that doesn't help, you camera is covered by Nikon's warranty. Contact Nikon Service at 1-800-NIKON-US (1-800-645-6687) 9AM-8PM EST, Monday to Friday.

Despite what Rajdeep says, the demo mode on the D3100 allows you to take a picture without a memory card and review it. This is primarily intended to let you see how the camera works --- a demonstration. If you want to get out of the demo mode, you must insert a memory card. Without a memory card, the camera has only enough memory to hold one picture, and this picture will disappear when you turn the camera off.

The demo mode is discussed (briefly) in the "Slot Empty Release Lock" section of the manual (page 147 in my copy).

Basically, you put batteries into the flash, put it into the flash mount on the top of the camera, turn everything on, select a flash mode, and start shooting.
The flash comes with a detailed manual describing its operation. There is a section in the camera manual describing the various flash modes. The SB-700 is fully compatible with the Nikon iCLS system, which includes the D3100.

Since you asked a general question, I can only give you a general answer. If you have any specific questions, please feel free to ask them.

For the Nikon D3100, there is a live view switch which is located on the mid-right side (please see image)

For Quick Response Mode and other Release Modes, please see "image1":

image 1


For remote control shooting or Bulb mode, see "image2":


image 2

Night mode?

Do you mean Night Portrait mode? Select it by turning the mode dial to the appropriate icon, deselect it by turning the mode dial to some other mode.

Do you mean flash? It pops up automatically in the point&shoot modes (except for Sports, Landscape, and NoFlash). You have to pop it up in PSAM modes.