Nikon d7000 broken autofocus Repair or Exchange after 4 day use?

I just purchased a brand new Nikon d7000 and after 4 days of use the Autofocus stopped working!

I was wondering which would be better? To send it to Nikon for Repair? Or To send it back to the Store for an Exchange? Why?

I worry on both because. I don't want to send it away for repair and have something else go wrong with it once I get it back… After all it doesn't really bode well to be having a brand new camera repaired after only 4 days use. And I also worry that if I exchange it I will end up with another problem camera! Thoughts?

Added (1). Did all the stuff both of you mentioned. Read through almost the whole manual, checked all the autofocus & lock buttons, checked All menu settings, even tried reattaching the lens again! Nothing! Won't focus.

The odds are that it's not bust at all, but that you've changed a setting or are doing something silly!

Make sure any MF/AF switches on the body and lens are set to AF (auto focus), and then go into the camera menus and find the reset option, to put all settings back to their factory defaults!

The D7000 is a great camera. First thing to do is read the first few pages of the owners manual to make sure it isn't user error. Check the settings on the side of the lens.
If all else fails, take it back to the store you bought it at. I have a Nikon N2000 I bought in 1986 that still works well.

If it's a walk-in store, go back and see if they can get it to work. If not, exchange it and let them deal with the hassle of a return to Nikon.

Also try a reset to factory defaults.
Be sure focus switch on the lens is set to auto.
Be sure the focus switch on the body near the lens mount is set to auto.
Be sure your lens is correctly locked in place. If locked in place, it won't rotate at the base.

You don't repair a less-than-a-week-old camera. You return it under warranty and have it replaced. I suggest you hurry back to the store you bought it from right away. Don't forget to bring the box and everything that came in it including the sales receipt. No receipt, no exchange.

Did you check to see to see if autofocus is assign to another button, Press the AE-L AF-L button on the back, or the function button, or the depth of preview button on the front and see if it will autofocus.