Nikon d5100 clicking only complete black images?

My d5100 just stopped taking pictures any pic i click would be shown as a black on screen… I just bought it a week ago… Wt to do?

Take it back to the retailer, if you bought it online contact them immediately

Check that you aren't shooting on Manual with your shutter speed too high.

No offense intended but I'm thinking you forgot to tell us you've been "messing with the settings" as people often say in here. If I'm right, then you need to look in the Owner's Manual and learn how to reset it to the factory defaults. If I'm wrong, then you need to take it back where you bought it and see if the camera is defective.

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

You also need to learn about the Exposure Triangle.
http://www.digital-photography-school.com/learning-exposure-in-digital-photography

No offence intended but starting from the total dummy end!
1) have you taken off the lens cap?- take it off!
2) have you turned off the display screen? Look at your manual - turn it back on
3) does the screen display the camera settings OK? - see 2. If it won't turn on take it to a Nikon dealer for repair.
4) are the photos black when you transfer them to the computer? If they are OK then see 2 & 3. If they are black - continue
5) have you set the camera to one of the advanced modes? If yes then set it to full auto and try again then see 6. If no - see 6
6) are the pictures black when you use full auto? If yes then the camera is broken - take it for repair under warranty. If they are OK then see 7
7) If the photos are only black when you are using one of the advanced modes then you are the problem:-) the camera is doing what you are telling it to do. Learn about exposure control and try again.