Nikon D3100 lens on Auto won't work?

I have a Nikon D3100 with a 55-300 and 18-55 lens. Whenever i have my my lens on auto, it won't shoot. And when its on Manual, it shoots fine but I'm not good at getting it focused in well. Any help/suggestions?

You are shooting too close to your subject. There's such a thing as minimum focusing distance. Have you read the manual already? I suggest you do.

There could be many reasons for this. In addition to the one above, you could be in a low light situation that does not present enough light for the autofocus to work, or you have the autofocus assist lamp turned off, you could have the focusing point setting incorrect for what you are trying to do, and so on.

The camera will not shoot because you are not focused, and this prevents you from having a bad photo.

Always try this test - especially if you are new to DSLRs and not sure what is happening.

Go outside on a bright sunny day, put the camera into AUTO mode, and see if you can take a good photo. If you can, there's something you are doing wrong. If it can't, then the camera may be broken.

But always try to reset the camera if all else fails before returning it for repair. There should be a reset procedure in your manual.