I just recently purchase a D3100. I have been teaching myself by reading the manual, various website DSLR articles and viewing videos. The Aperture setting (fstop), Shutter speed setting (how fast the shutter blinks) and Film speed (ISO) setting is the heart of your ability as a photographer to be creative. If the person who used the camera was adjusting these settings to be creative then you will probably get blurry or otherwise unsatisfactory pictures unless you change the settings to suit the picture you were taking. The catch-all here is go back to the auto setting until you learn how to use the camera manually. (Also, go back over the manual and redo the setting if necessary.The camera does all the work for you.) Press the shutter button half way down to adjust the lense focus and when your satisfied, shoot. I hope this helps you because this has happened to me as well. I learned how to manually control my camera. It is fun to try different settings and see what they can do to the picture result. If all else fails go to auto mode and shoot away. There is no shame in that.