My shutter speed isn't the same time as what i'm setting on my camera?

I noticed this. That in Shutter or manual mode when i'm taking pictures. My shutter speed, if I set it to 30 seconds for example. It closes in 10 seconds, 11 seconds. Or anything I have not set! It's just lesser for lesser times.a 5 second exposure becomes 1 or 2 seconds. Can anyone tell me what's wrong? I'm using a Nikon D5100.

Added (1). And my camera is in good condition. Just a few months old. I use it occasionally.never dropped it.didn't expose it to any damage. Only connect to my laptop for transferring pictures.used the memory card to load picture controls. Thats all.

Hmm, check and make sure the camera is in full manual mode (M)
Your camera may be adjusting shutter speed to compensate for over exposure.

There's a master reset for your camera that resets everything back to factory defaults. You may have set something incorrectly. Try resetting your camera and see what happens.

Sounds like you need to send it back to the maker - under warranty…

There are a couple of things to check. First, if you want full control you need to refer to your manual and turn off some items that will affect automatic functions. Second, I once had a similar problem on a different DSLR. It turned out that I hadn't paid attention to my battery level and it was low enough that it would pull it down under load to a point where the camera was sensing the problem and completing the capture early to avoid completely loosing the image. I hope this helps you out. This can be especially pronounced in cold weather with long exposures.

Only in Manual Mode (M on the Mode dial) will your camera use the shutter speed you select, all other modes (P, Av, Tv) are Auto Modes and it will alter it to get a correct(ish) exposure.

Make sure the EV compensation is on zero as that will override any auto setting.

In Shutter Priority you select a shutter speed and the camera will select an aperture that will produce an acceptable exposure. If you select a 30 second shutter speed and the lens only stops down to f32 the camera will over-ride the shutter speed you chose and use one that will give an acceptable exposure.

If you're in Manual Mode - which I rather doubt - then you can set any shutter speed and aperture you want but more than likely you'll end up with a very underexposed or very overexposed image if you aren't using the camera's built-in light meter.

On a sunny day using ISO 100 a 30 second exposure would require an aperture of f720 to achieve a correct exposure. This can be proven by using an old rule invented before cameras had built-in light meters - the "Sunny 16 Rule".It states: "On a sunny day, set your aperture to f16 and your shutter speed to 1/ISO." Here is what an exposure chart based on ISO 100 would look like on a sunny day:

ISO 100
f720 @ 30 seconds. -11 stops
f512 @ 15 seconds. -10 stops
f360 @ 8 seconds. -9 stops
f256 @ 4 seconds. -8 stops
f180 @ 2 seconds. -7 stops
f128 @ 1 second. -6 stops
f90 @ 1/3 sec. -5 stops
f64 @ 1/6 sec. -4 stops
f45 @ 1/12 sec. -3 stops
f32 @ 1/25 sec. -2 stops
f22 @ 1/50 sec. -1 stop
f16 @ 1/100 sec. "Sunny 16"

Although some lenses do stop down to f32, any further reduction in light transmission will require use of a Neutral Density filter.http://en.wikipedia.org/wiki/Neutral_density_filter

You simply can't arbitrarily set an aperture and shutter speed and ignore the camera's light meter and expect good results. If you have your camera in full Manual Mode and select f32 and a 30 second exposure all you'll get is a very black image due to gross overexposure. If you select f32 and a 1/1000 sec.shutter speed all you'll get is a very white image due to gross underexposure.

This will help you learn about exposure:
http://www.digital-photography-school.com/learning-exposure-in-digital-photography

This will help you learn to use your Nikon D5100:
http://www.nikondigitutor.com/eng/d5100/index.html Who better than Nikon to teach you to use your Nikon D5100?

Check you haven't got Auto Exposure Bracketing (AEB) or exposure compensation (EV) turned on.